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 $59.91   6.653%   $63.8958   $63.90   $63.90   $63.90  
  Purchase #2 $196.72   13.722%   $223.7139   $223.71   $223.70   $223.70  
  Purchase #3 $22.55   13.296%   $25.5482   $25.55   $25.55   $25.50  
  Purchase #4 $31.71   13.430%   $35.9687   $35.97   $35.95   $36.00  
  Purchase #5 $218.42   5.742%   $230.9617   $230.96   $230.95   $231.00  
  Purchase #6 $174.31   13.132%   $197.2004   $197.20   $197.20   $197.20  
  Purchase #7 $165.40   9.559%   $181.2106   $181.21   $181.20   $181.20  
  7 purchase totals = $869.02       $958.4993   $958.50   $958.45   $958.50