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 $54.67   12.237%   $61.36   $61.36   $61.35   $61.40  
  Purchase #2 $244.57   12.451%   $275.0214   $275.02   $275.00   $275.00  
  Purchase #3 $116.53   9.618%   $127.7379   $127.74   $127.75   $127.70  
  Purchase #4 $172.80   9.356%   $188.9672   $188.97   $188.95   $189.00  
  Purchase #5 $135.40   3.786%   $140.5262   $140.53   $140.55   $140.50  
  Purchase #6 $238.49   5.501%   $251.6093   $251.61   $251.60   $251.60  
  Purchase #7 $215.79   3.211%   $222.719   $222.72   $222.70   $222.70  
  7 purchase totals = $1,178.25       $1,267.9410   $1,267.95   $1,267.90   $1,267.90