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 $114.66   4.465%   $119.7796   $119.78   $119.80   $119.80  
  Purchase #2 $136.42   8.219%   $147.6324   $147.63   $147.65   $147.60  
  Purchase #3 $17.52   7.703%   $18.8696   $18.87   $18.85   $18.90  
  Purchase #4 $189.30   4.556%   $197.9245   $197.92   $197.90   $197.90  
  Purchase #5 $110.32   7.364%   $118.444   $118.44   $118.45   $118.40  
  Purchase #6 $102.43   8.410%   $111.0444   $111.04   $111.05   $111.00  
  Purchase #7 $246.77   4.449%   $257.7488   $257.75   $257.75   $257.70  
  7 purchase totals = $917.42       $971.4433   $971.43   $971.45   $971.30