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 $210.45   6.530%   $224.1924   $224.19   $224.20   $224.20  
  Purchase #2 $117.39   13.177%   $132.8585   $132.86   $132.85   $132.90  
  Purchase #3 $97.35   13.528%   $110.5195   $110.52   $110.50   $110.50  
  Purchase #4 $75.39   13.858%   $85.8375   $85.84   $85.85   $85.80  
  Purchase #5 $206.67   8.558%   $224.3568   $224.36   $224.35   $224.40  
  Purchase #6 $236.80   9.104%   $258.3583   $258.36   $258.35   $258.40  
  Purchase #7 $16.55   13.112%   $18.72   $18.72   $18.70   $18.70  
  7 purchase totals = $960.60       $1,054.8430   $1,054.85   $1,054.80   $1,054.90