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 $76.42   8.586%   $82.9814   $82.98   $83.00   $83.00  
  Purchase #2 $226.43   11.784%   $253.1125   $253.11   $253.10   $253.10  
  Purchase #3 $123.47   9.183%   $134.8083   $134.81   $134.80   $134.80  
  Purchase #4 $202.27   13.472%   $229.5198   $229.52   $229.50   $229.50  
  Purchase #5 $170.77   10.792%   $189.1995   $189.20   $189.20   $189.20  
  Purchase #6 $80.91   4.735%   $84.7411   $84.74   $84.75   $84.70  
  Purchase #7 $87.47   12.811%   $98.6758   $98.68   $98.70   $98.70  
  7 purchase totals = $967.74       $1,073.0384   $1,073.04   $1,073.05   $1,073.00