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 $61.54   13.482%   $69.8368   $69.84   $69.85   $69.80  
  Purchase #2 $207.56   8.119%   $224.4118   $224.41   $224.40   $224.40  
  Purchase #3 $24.34   10.462%   $26.8865   $26.89   $26.90   $26.90  
  Purchase #4 $91.69   11.330%   $102.0785   $102.08   $102.10   $102.10  
  Purchase #5 $244.78   6.402%   $260.4508   $260.45   $260.45   $260.50  
  Purchase #6 $137.33   11.441%   $153.0419   $153.04   $153.05   $153.00  
  Purchase #7 $167.67   9.693%   $183.9223   $183.92   $183.90   $183.90  
  7 purchase totals = $934.91       $1,020.6286   $1,020.63   $1,020.65   $1,020.60