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 $88.71   5.187%   $93.3114   $93.31   $93.30   $93.30  
  Purchase #2 $175.70   9.269%   $191.9856   $191.99   $192.00   $192.00  
  Purchase #3 $187.32   13.696%   $212.9753   $212.98   $213.00   $213.00  
  Purchase #4 $224.52   4.682%   $235.032   $235.03   $235.05   $235.00  
  Purchase #5 $199.76   3.275%   $206.3021   $206.30   $206.30   $206.30  
  Purchase #6 $53.41   7.771%   $57.5605   $57.56   $57.55   $57.60  
  Purchase #7 $243.64   5.471%   $256.9695   $256.97   $256.95   $257.00  
  7 purchase totals = $1,173.06       $1,254.1364   $1,254.14   $1,254.15   $1,254.20