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 $26.45   3.268%   $27.3144   $27.31   $27.30   $27.30  
  Purchase #2 $192.96   4.857%   $202.3321   $202.33   $202.35   $202.30  
  Purchase #3 $197.50   5.160%   $207.691   $207.69   $207.70   $207.70  
  Purchase #4 $43.27   5.392%   $45.6031   $45.60   $45.60   $45.60  
  Purchase #5 $68.95   11.827%   $77.1047   $77.10   $77.10   $77.10  
  Purchase #6 $210.92   7.123%   $225.9438   $225.94   $225.95   $225.90  
  Purchase #7 $222.77   6.733%   $237.7691   $237.77   $237.75   $237.80  
  7 purchase totals = $962.82       $1,023.7582   $1,023.74   $1,023.75   $1,023.70