Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $167.61   11.835%   $187.4466   $187.45   $187.45   $187.40  
  Purchase #2 $137.40   3.249%   $141.8641   $141.86   $141.85   $141.90  
  Purchase #3 $235.61   12.297%   $264.583   $264.58   $264.60   $264.60  
  Purchase #4 $192.52   5.181%   $202.4945   $202.49   $202.50   $202.50  
  Purchase #5 $100.81   8.802%   $109.6833   $109.68   $109.70   $109.70  
  Purchase #6 $116.51   9.689%   $127.7987   $127.80   $127.80   $127.80  
  Purchase #7 $209.39   11.818%   $234.1357   $234.14   $234.15   $234.10  
  7 purchase totals = $1,159.85       $1,268.0059   $1,268.00   $1,268.05   $1,268.00