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 $241.34   10.874%   $267.5833   $267.58   $267.60   $267.60  
  Purchase #2 $228.32   3.313%   $235.8842   $235.88   $235.90   $235.90  
  Purchase #3 $139.40   8.663%   $151.4762   $151.48   $151.50   $151.50  
  Purchase #4 $237.93   12.485%   $267.6356   $267.64   $267.65   $267.60  
  Purchase #5 $56.82   6.279%   $60.3877   $60.39   $60.40   $60.40  
  Purchase #6 $48.74   11.788%   $54.4855   $54.49   $54.50   $54.50  
  Purchase #7 $204.69   10.185%   $225.5377   $225.54   $225.55   $225.50  
  7 purchase totals = $1,157.24       $1,262.9902   $1,263.00   $1,263.10   $1,263.00