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 $245.39   12.456%   $275.9558   $275.96   $275.95   $276.00  
  Purchase #2 $241.33   8.145%   $260.9863   $260.99   $261.00   $261.00  
  Purchase #3 $223.58   4.817%   $234.3498   $234.35   $234.35   $234.30  
  Purchase #4 $40.30   6.636%   $42.9743   $42.97   $42.95   $43.00  
  Purchase #5 $162.98   4.701%   $170.6417   $170.64   $170.65   $170.60  
  Purchase #6 $134.40   12.833%   $151.6476   $151.65   $151.65   $151.60  
  Purchase #7 $13.78   6.828%   $14.7209   $14.72   $14.70   $14.70  
  7 purchase totals = $1,061.76       $1,151.2764   $1,151.28   $1,151.25   $1,151.20