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 $71.57   5.279%   $75.3482   $75.35   $75.35   $75.30  
  Purchase #2 $159.52   8.668%   $173.3472   $173.35   $173.35   $173.30  
  Purchase #3 $217.99   6.569%   $232.3098   $232.31   $232.30   $232.30  
  Purchase #4 $185.69   9.173%   $202.7233   $202.72   $202.70   $202.70  
  Purchase #5 $168.75   6.606%   $179.8976   $179.90   $179.90   $179.90  
  Purchase #6 $26.93   4.457%   $28.1303   $28.13   $28.15   $28.10  
  Purchase #7 $121.56   6.729%   $129.7398   $129.74   $129.75   $129.70  
  7 purchase totals = $952.01       $1,021.4962   $1,021.50   $1,021.50   $1,021.30