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 $210.60   10.154%   $231.9843   $231.98   $232.00   $232.00  
  Purchase #2 $107.43   9.479%   $117.6133   $117.61   $117.60   $117.60  
  Purchase #3 $74.39   11.127%   $82.6674   $82.67   $82.65   $82.70  
  Purchase #4 $128.64   8.731%   $139.8716   $139.87   $139.85   $139.90  
  Purchase #5 $241.60   12.732%   $272.3605   $272.36   $272.35   $272.40  
  Purchase #6 $35.65   10.603%   $39.43   $39.43   $39.45   $39.40  
  Purchase #7 $59.84   12.578%   $67.3667   $67.37   $67.35   $67.40  
  7 purchase totals = $858.15       $951.2938   $951.29   $951.25   $951.40