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 $69.85   4.780%   $73.1888   $73.19   $73.20   $73.20  
  Purchase #2 $51.39   8.305%   $55.6579   $55.66   $55.65   $55.70  
  Purchase #3 $104.72   11.603%   $116.8707   $116.87   $116.85   $116.90  
  Purchase #4 $19.46   13.345%   $22.0569   $22.06   $22.05   $22.10  
  Purchase #5 $181.89   11.353%   $202.54   $202.54   $202.55   $202.50  
  Purchase #6 $16.84   6.305%   $17.9018   $17.90   $17.90   $17.90  
  Purchase #7 $167.83   7.793%   $180.909   $180.91   $180.90   $180.90  
  7 purchase totals = $611.98       $669.1251   $669.13   $669.10   $669.20