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 $112.74   8.462%   $122.2801   $122.28   $122.30   $122.30  
  Purchase #2 $101.95   6.635%   $108.7144   $108.71   $108.70   $108.70  
  Purchase #3 $206.35   6.512%   $219.7875   $219.79   $219.80   $219.80  
  Purchase #4 $212.97   11.137%   $236.6885   $236.69   $236.70   $236.70  
  Purchase #5 $58.44   5.484%   $61.6448   $61.64   $61.65   $61.60  
  Purchase #6 $232.57   9.267%   $254.1223   $254.12   $254.10   $254.10  
  Purchase #7 $57.61   4.572%   $60.2439   $60.24   $60.25   $60.20  
  7 purchase totals = $982.63       $1,063.4815   $1,063.47   $1,063.50   $1,063.40