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 $56.42   11.227%   $62.7543   $62.75   $62.75   $62.80  
  Purchase #2 $194.87   5.158%   $204.9214   $204.92   $204.90   $204.90  
  Purchase #3 $214.52   6.485%   $228.4316   $228.43   $228.45   $228.40  
  Purchase #4 $181.30   4.134%   $188.7949   $188.79   $188.80   $188.80  
  Purchase #5 $76.90   13.192%   $87.0446   $87.04   $87.05   $87.00  
  Purchase #6 $112.42   3.317%   $116.149   $116.15   $116.15   $116.10  
  Purchase #7 $181.45   4.811%   $190.1796   $190.18   $190.20   $190.20  
  7 purchase totals = $1,017.88       $1,078.2754   $1,078.26   $1,078.30   $1,078.20