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 $54.99   9.432%   $60.1767   $60.18   $60.20   $60.20  
  Purchase #2 $219.79   8.305%   $238.0436   $238.04   $238.05   $238.00  
  Purchase #3 $245.26   3.551%   $253.9692   $253.97   $253.95   $254.00  
  Purchase #4 $82.29   12.232%   $92.3557   $92.36   $92.35   $92.40  
  Purchase #5 $148.55   7.753%   $160.0671   $160.07   $160.05   $160.10  
  Purchase #6 $153.85   5.286%   $161.9825   $161.98   $162.00   $162.00  
  Purchase #7 $33.73   9.586%   $36.9634   $36.96   $36.95   $37.00  
  7 purchase totals = $938.46       $1,003.5582   $1,003.56   $1,003.55   $1,003.70