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 $223.80   13.561%   $254.1495   $254.15   $254.15   $254.10  
  Purchase #2 $121.52   9.203%   $132.7035   $132.70   $132.70   $132.70  
  Purchase #3 $142.44   6.861%   $152.2128   $152.21   $152.20   $152.20  
  Purchase #4 $230.58   11.765%   $257.7077   $257.71   $257.70   $257.70  
  Purchase #5 $14.49   12.351%   $16.2797   $16.28   $16.30   $16.30  
  Purchase #6 $70.95   6.555%   $75.6008   $75.60   $75.60   $75.60  
  Purchase #7 $62.41   8.289%   $67.5832   $67.58   $67.60   $67.60  
  7 purchase totals = $866.19       $956.2372   $956.23   $956.25   $956.20