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 $191.82   8.312%   $207.7641   $207.76   $207.75   $207.80  
  Purchase #2 $227.35   10.777%   $251.8515   $251.85   $251.85   $251.90  
  Purchase #3 $132.87   4.571%   $138.9435   $138.94   $138.95   $138.90  
  Purchase #4 $193.72   4.146%   $201.7516   $201.75   $201.75   $201.80  
  Purchase #5 $146.80   3.341%   $151.7046   $151.70   $151.70   $151.70  
  Purchase #6 $244.52   7.442%   $262.7172   $262.72   $262.70   $262.70  
  Purchase #7 $250.98   6.295%   $266.7792   $266.78   $266.80   $266.80  
  7 purchase totals = $1,388.06       $1,481.5117   $1,481.50   $1,481.50   $1,481.60