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 $58.96   10.824%   $65.3418   $65.34   $65.35   $65.30  
  Purchase #2 $77.53   8.634%   $84.2239   $84.22   $84.20   $84.20  
  Purchase #3 $155.41   5.484%   $163.9327   $163.93   $163.95   $163.90  
  Purchase #4 $148.57   5.284%   $156.4204   $156.42   $156.40   $156.40  
  Purchase #5 $105.80   3.527%   $109.5316   $109.53   $109.55   $109.50  
  Purchase #6 $246.73   4.640%   $258.1783   $258.18   $258.20   $258.20  
  Purchase #7 $235.34   3.685%   $244.0123   $244.01   $244.00   $244.00  
  7 purchase totals = $1,028.34       $1,081.6410   $1,081.63   $1,081.65   $1,081.50