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 $52.35   12.782%   $59.0414   $59.04   $59.05   $59.00  
  Purchase #2 $168.80   9.861%   $185.4454   $185.45   $185.45   $185.40  
  Purchase #3 $135.93   11.728%   $151.8719   $151.87   $151.85   $151.90  
  Purchase #4 $95.59   9.368%   $104.5449   $104.54   $104.55   $104.50  
  Purchase #5 $191.83   3.201%   $197.9705   $197.97   $197.95   $198.00  
  Purchase #6 $190.51   5.652%   $201.2776   $201.28   $201.30   $201.30  
  Purchase #7 $50.84   6.383%   $54.0851   $54.09   $54.10   $54.10  
  7 purchase totals = $885.85       $954.2368   $954.24   $954.25   $954.20