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 $207.64   10.102%   $228.6158   $228.62   $228.60   $228.60  
  Purchase #2 $219.84   6.842%   $234.8815   $234.88   $234.90   $234.90  
  Purchase #3 $7.93   3.674%   $8.2213   $8.22   $8.20   $8.20  
  Purchase #4 $228.36   10.467%   $252.2624   $252.26   $252.25   $252.30  
  Purchase #5 $163.42   5.228%   $171.9636   $171.96   $171.95   $172.00  
  Purchase #6 $140.88   9.333%   $154.0283   $154.03   $154.05   $154.00  
  Purchase #7 $9.56   6.181%   $10.1509   $10.15   $10.15   $10.20  
  7 purchase totals = $977.63       $1,060.1238   $1,060.12   $1,060.10   $1,060.20