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 $219.78   6.832%   $234.7954   $234.80   $234.80   $234.80  
  Purchase #2 $115.36   8.751%   $125.4552   $125.46   $125.45   $125.50  
  Purchase #3 $45.72   10.363%   $50.458   $50.46   $50.45   $50.50  
  Purchase #4 $24.60   3.679%   $25.505   $25.51   $25.50   $25.50  
  Purchase #5 $184.37   13.725%   $209.6748   $209.67   $209.65   $209.70  
  Purchase #6 $64.60   6.792%   $68.9876   $68.99   $69.00   $69.00  
  Purchase #7 $217.39   6.337%   $231.166   $231.17   $231.15   $231.20  
  7 purchase totals = $871.82       $946.0420   $946.06   $946.00   $946.20