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 $198.94   8.593%   $216.0349   $216.03   $216.05   $216.00  
  Purchase #2 $160.88   6.823%   $171.8568   $171.86   $171.85   $171.90  
  Purchase #3 $39.34   11.870%   $44.0097   $44.01   $44.00   $44.00  
  Purchase #4 $130.93   7.842%   $141.1975   $141.20   $141.20   $141.20  
  Purchase #5 $179.86   12.669%   $202.6465   $202.65   $202.65   $202.60  
  Purchase #6 $149.30   13.796%   $169.8974   $169.90   $169.90   $169.90  
  Purchase #7 $220.80   12.153%   $247.6338   $247.63   $247.65   $247.60  
  7 purchase totals = $1,080.05       $1,193.2766   $1,193.28   $1,193.30   $1,193.20