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 $186.92   8.564%   $202.9278   $202.93   $202.95   $202.90  
  Purchase #2 $6.48   9.565%   $7.0998   $7.10   $7.10   $7.10  
  Purchase #3 $108.88   5.626%   $115.0056   $115.01   $115.00   $115.00  
  Purchase #4 $124.53   4.859%   $130.5809   $130.58   $130.60   $130.60  
  Purchase #5 $183.82   12.561%   $206.9096   $206.91   $206.90   $206.90  
  Purchase #6 $219.53   8.344%   $237.8476   $237.85   $237.85   $237.80  
  Purchase #7 $23.88   8.237%   $25.847   $25.85   $25.85   $25.80  
  7 purchase totals = $854.04       $926.2183   $926.23   $926.25   $926.10