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 $212.96   8.807%   $231.7154   $231.72   $231.70   $231.70  
  Purchase #2 $232.46   6.677%   $247.9814   $247.98   $248.00   $248.00  
  Purchase #3 $35.66   12.660%   $40.1746   $40.17   $40.15   $40.20  
  Purchase #4 $61.68   11.790%   $68.9521   $68.95   $68.95   $69.00  
  Purchase #5 $200.60   3.610%   $207.8417   $207.84   $207.85   $207.80  
  Purchase #6 $64.93   3.643%   $67.2954   $67.30   $67.30   $67.30  
  Purchase #7 $150.91   12.861%   $170.3185   $170.32   $170.30   $170.30  
  7 purchase totals = $959.20       $1,034.2791   $1,034.28   $1,034.25   $1,034.30