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 $70.82   4.484%   $73.9956   $74.00   $74.00   $74.00  
  Purchase #2 $212.39   11.753%   $237.3522   $237.35   $237.35   $237.40  
  Purchase #3 $156.65   4.682%   $163.9844   $163.98   $164.00   $164.00  
  Purchase #4 $148.55   10.121%   $163.5847   $163.58   $163.60   $163.60  
  Purchase #5 $162.48   6.616%   $173.2297   $173.23   $173.25   $173.20  
  Purchase #6 $197.69   13.306%   $223.9946   $223.99   $224.00   $224.00  
  Purchase #7 $169.38   12.753%   $190.981   $190.98   $191.00   $191.00  
  7 purchase totals = $1,117.96       $1,227.1222   $1,227.11   $1,227.20   $1,227.20