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 $61.67   5.430%   $65.0187   $65.02   $65.00   $65.00  
  Purchase #2 $233.37   9.181%   $254.7957   $254.80   $254.80   $254.80  
  Purchase #3 $59.92   11.859%   $67.0259   $67.03   $67.05   $67.00  
  Purchase #4 $150.94   6.355%   $160.5322   $160.53   $160.55   $160.50  
  Purchase #5 $28.32   5.440%   $29.8606   $29.86   $29.85   $29.90  
  Purchase #6 $34.48   13.679%   $39.1965   $39.20   $39.20   $39.20  
  Purchase #7 $238.38   11.790%   $266.485   $266.49   $266.50   $266.50  
  7 purchase totals = $807.08       $882.9146   $882.93   $882.95   $882.90