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 $187.82   8.471%   $203.7302   $203.73   $203.75   $203.70  
  Purchase #2 $228.45   7.175%   $244.8413   $244.84   $244.85   $244.80  
  Purchase #3 $59.61   4.230%   $62.1315   $62.13   $62.15   $62.10  
  Purchase #4 $212.34   4.126%   $221.1011   $221.10   $221.10   $221.10  
  Purchase #5 $136.90   5.123%   $143.9134   $143.91   $143.90   $143.90  
  Purchase #6 $142.53   13.663%   $162.0039   $162.00   $162.00   $162.00  
  Purchase #7 $200.51   10.504%   $221.5716   $221.57   $221.55   $221.60  
  7 purchase totals = $1,168.16       $1,259.2930   $1,259.28   $1,259.30   $1,259.20