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 $84.58   10.267%   $93.2638   $93.26   $93.25   $93.30  
  Purchase #2 $58.69   7.421%   $63.0454   $63.05   $63.05   $63.00  
  Purchase #3 $35.52   5.546%   $37.4899   $37.49   $37.50   $37.50  
  Purchase #4 $81.57   11.145%   $90.661   $90.66   $90.65   $90.70  
  Purchase #5 $160.87   9.751%   $176.5564   $176.56   $176.55   $176.60  
  Purchase #6 $33.28   3.529%   $34.4545   $34.45   $34.45   $34.50  
  Purchase #7 $249.28   7.646%   $268.3399   $268.34   $268.35   $268.30  
  7 purchase totals = $703.79       $763.8109   $763.81   $763.80   $763.90