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 $93.62   5.302%   $98.5837   $98.58   $98.60   $98.60  
  Purchase #2 $93.83   10.230%   $103.4288   $103.43   $103.45   $103.40  
  Purchase #3 $98.43   5.534%   $103.8771   $103.88   $103.90   $103.90  
  Purchase #4 $194.45   3.702%   $201.6485   $201.65   $201.65   $201.60  
  Purchase #5 $149.93   6.687%   $159.9558   $159.96   $159.95   $160.00  
  Purchase #6 $23.38   13.402%   $26.5134   $26.51   $26.50   $26.50  
  Purchase #7 $184.37   7.818%   $198.784   $198.78   $198.80   $198.80  
  7 purchase totals = $838.01       $892.7913   $892.79   $892.85   $892.80