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 $53.96   11.824%   $60.3402   $60.34   $60.35   $60.30  
  Purchase #2 $147.43   8.526%   $159.9999   $160.00   $160.00   $160.00  
  Purchase #3 $215.54   6.116%   $228.7224   $228.72   $228.70   $228.70  
  Purchase #4 $44.55   3.495%   $46.107   $46.11   $46.10   $46.10  
  Purchase #5 $233.86   8.546%   $253.8457   $253.85   $253.85   $253.80  
  Purchase #6 $234.36   4.584%   $245.1031   $245.10   $245.10   $245.10  
  Purchase #7 $230.30   10.443%   $254.3502   $254.35   $254.35   $254.40  
  7 purchase totals = $1,160.00       $1,248.4685   $1,248.47   $1,248.45   $1,248.40