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 $88.95   8.252%   $96.2902   $96.29   $96.30   $96.30  
  Purchase #2 $37.94   6.199%   $40.2919   $40.29   $40.30   $40.30  
  Purchase #3 $41.87   13.264%   $47.4236   $47.42   $47.40   $47.40  
  Purchase #4 $152.90   7.272%   $164.0189   $164.02   $164.00   $164.00  
  Purchase #5 $55.67   13.157%   $62.9945   $62.99   $63.00   $63.00  
  Purchase #6 $161.93   13.140%   $183.2076   $183.21   $183.20   $183.20  
  Purchase #7 $162.99   8.339%   $176.5817   $176.58   $176.60   $176.60  
  7 purchase totals = $702.25       $770.8084   $770.80   $770.80   $770.80