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 $158.58   9.802%   $174.124   $174.12   $174.10   $174.10  
  Purchase #2 $47.60   11.148%   $52.9064   $52.91   $52.90   $52.90  
  Purchase #3 $89.30   8.592%   $96.9727   $96.97   $96.95   $97.00  
  Purchase #4 $205.39   4.613%   $214.8646   $214.86   $214.85   $214.90  
  Purchase #5 $21.89   13.618%   $24.871   $24.87   $24.85   $24.90  
  Purchase #6 $229.91   4.829%   $241.0124   $241.01   $241.00   $241.00  
  Purchase #7 $152.49   6.222%   $161.9779   $161.98   $162.00   $162.00  
  7 purchase totals = $905.16       $966.7290   $966.72   $966.65   $966.80