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 $226.33   12.234%   $254.0192   $254.02   $254.00   $254.00  
  Purchase #2 $201.71   13.639%   $229.2212   $229.22   $229.20   $229.20  
  Purchase #3 $202.73   4.794%   $212.4489   $212.45   $212.45   $212.40  
  Purchase #4 $45.98   7.186%   $49.2841   $49.28   $49.30   $49.30  
  Purchase #5 $194.33   6.108%   $206.1997   $206.20   $206.20   $206.20  
  Purchase #6 $152.52   7.215%   $163.5243   $163.52   $163.50   $163.50  
  Purchase #7 $61.69   7.210%   $66.1378   $66.14   $66.15   $66.10  
  7 purchase totals = $1,085.29       $1,180.8352   $1,180.83   $1,180.80   $1,180.70