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 $83.77   13.708%   $95.2532   $95.25   $95.25   $95.30  
  Purchase #2 $48.77   4.212%   $50.8242   $50.82   $50.80   $50.80  
  Purchase #3 $53.65   6.214%   $56.9838   $56.98   $57.00   $57.00  
  Purchase #4 $188.57   7.389%   $202.5034   $202.50   $202.50   $202.50  
  Purchase #5 $162.64   13.456%   $184.5248   $184.52   $184.50   $184.50  
  Purchase #6 $41.98   7.107%   $44.9635   $44.96   $44.95   $45.00  
  Purchase #7 $74.52   5.607%   $78.6983   $78.70   $78.70   $78.70  
  7 purchase totals = $653.90       $713.7512   $713.73   $713.70   $713.80