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 $244.74   12.406%   $275.1024   $275.10   $275.10   $275.10  
  Purchase #2 $133.60   4.457%   $139.5546   $139.55   $139.55   $139.60  
  Purchase #3 $61.75   11.121%   $68.6172   $68.62   $68.60   $68.60  
  Purchase #4 $200.39   11.126%   $222.6854   $222.69   $222.70   $222.70  
  Purchase #5 $166.61   9.490%   $182.4213   $182.42   $182.40   $182.40  
  Purchase #6 $245.64   11.692%   $274.3602   $274.36   $274.35   $274.40  
  Purchase #7 $182.96   6.258%   $194.4096   $194.41   $194.40   $194.40  
  7 purchase totals = $1,235.69       $1,357.1507   $1,357.15   $1,357.10   $1,357.20