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 $225.83   12.819%   $254.7791   $254.78   $254.80   $254.80  
  Purchase #2 $41.73   5.792%   $44.147   $44.15   $44.15   $44.10  
  Purchase #3 $23.31   13.376%   $26.4279   $26.43   $26.45   $26.40  
  Purchase #4 $132.77   6.814%   $141.8169   $141.82   $141.80   $141.80  
  Purchase #5 $66.86   9.335%   $73.1014   $73.10   $73.10   $73.10  
  Purchase #6 $249.82   4.710%   $261.5865   $261.59   $261.60   $261.60  
  Purchase #7 $220.74   6.694%   $235.5163   $235.52   $235.50   $235.50  
  7 purchase totals = $961.06       $1,037.3751   $1,037.39   $1,037.40   $1,037.30