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 $106.46   10.151%   $117.2668   $117.27   $117.25   $117.30  
  Purchase #2 $22.91   6.674%   $24.439   $24.44   $24.45   $24.40  
  Purchase #3 $43.47   12.290%   $48.8125   $48.81   $48.80   $48.80  
  Purchase #4 $133.97   3.183%   $138.2343   $138.23   $138.25   $138.20  
  Purchase #5 $231.40   9.742%   $253.943   $253.94   $253.95   $253.90  
  Purchase #6 $157.74   12.764%   $177.8739   $177.87   $177.85   $177.90  
  Purchase #7 $241.70   12.548%   $272.0285   $272.03   $272.05   $272.00  
  7 purchase totals = $937.65       $1,032.5980   $1,032.59   $1,032.60   $1,032.50