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 $63.59   7.614%   $68.4317   $68.43   $68.45   $68.40  
  Purchase #2 $95.46   7.607%   $102.7216   $102.72   $102.70   $102.70  
  Purchase #3 $160.45   5.384%   $169.0886   $169.09   $169.10   $169.10  
  Purchase #4 $238.53   9.761%   $261.8129   $261.81   $261.80   $261.80  
  Purchase #5 $165.74   8.138%   $179.2279   $179.23   $179.25   $179.20  
  Purchase #6 $60.72   5.127%   $63.8331   $63.83   $63.85   $63.80  
  Purchase #7 $89.61   10.717%   $99.2135   $99.21   $99.20   $99.20  
  7 purchase totals = $874.10       $944.3293   $944.32   $944.35   $944.20