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 $193.42   5.731%   $204.5049   $204.50   $204.50   $204.50  
  Purchase #2 $31.46   12.523%   $35.3997   $35.40   $35.40   $35.40  
  Purchase #3 $85.28   4.146%   $88.8157   $88.82   $88.80   $88.80  
  Purchase #4 $75.46   5.436%   $79.562   $79.56   $79.55   $79.60  
  Purchase #5 $75.90   11.761%   $84.8266   $84.83   $84.85   $84.80  
  Purchase #6 $30.75   13.263%   $34.8284   $34.83   $34.85   $34.80  
  Purchase #7 $148.68   4.495%   $155.3632   $155.36   $155.35   $155.40  
  7 purchase totals = $640.95       $683.3005   $683.30   $683.30   $683.30