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 $166.60   5.552%   $175.8496   $175.85   $175.85   $175.80  
  Purchase #2 $137.45   12.417%   $154.5172   $154.52   $154.50   $154.50  
  Purchase #3 $217.41   13.398%   $246.5386   $246.54   $246.55   $246.50  
  Purchase #4 $159.70   5.836%   $169.0201   $169.02   $169.00   $169.00  
  Purchase #5 $94.50   10.432%   $104.3582   $104.36   $104.35   $104.40  
  Purchase #6 $64.55   8.475%   $70.0206   $70.02   $70.00   $70.00  
  Purchase #7 $7.96   8.327%   $8.6228   $8.62   $8.60   $8.60  
  7 purchase totals = $848.17       $928.9271   $928.93   $928.85   $928.80