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 $102.76   12.636%   $115.7448   $115.74   $115.75   $115.70  
  Purchase #2 $139.43   7.425%   $149.7827   $149.78   $149.80   $149.80  
  Purchase #3 $214.46   10.724%   $237.4587   $237.46   $237.45   $237.50  
  Purchase #4 $214.61   6.513%   $228.5875   $228.59   $228.60   $228.60  
  Purchase #5 $31.34   3.853%   $32.5475   $32.55   $32.55   $32.50  
  Purchase #6 $48.41   9.649%   $53.0811   $53.08   $53.10   $53.10  
  Purchase #7 $97.61   10.824%   $108.1753   $108.18   $108.20   $108.20  
  7 purchase totals = $848.62       $925.3776   $925.38   $925.45   $925.40