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 $144.61   5.198%   $152.1268   $152.13   $152.15   $152.10  
  Purchase #2 $138.96   5.723%   $146.9127   $146.91   $146.90   $146.90  
  Purchase #3 $56.26   6.531%   $59.9343   $59.93   $59.95   $59.90  
  Purchase #4 $202.79   5.184%   $213.3026   $213.30   $213.30   $213.30  
  Purchase #5 $243.68   11.700%   $272.1906   $272.19   $272.20   $272.20  
  Purchase #6 $5.96   8.840%   $6.4869   $6.49   $6.50   $6.50  
  Purchase #7 $158.75   5.830%   $168.0051   $168.01   $168.00   $168.00  
  7 purchase totals = $951.01       $1,018.9590   $1,018.96   $1,019.00   $1,018.90