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 $155.98   12.769%   $175.8971   $175.90   $175.90   $175.90  
  Purchase #2 $242.53   11.297%   $269.9286   $269.93   $269.95   $269.90  
  Purchase #3 $19.74   7.261%   $21.1733   $21.17   $21.15   $21.20  
  Purchase #4 $102.41   5.379%   $107.9186   $107.92   $107.90   $107.90  
  Purchase #5 $226.66   13.127%   $256.4137   $256.41   $256.40   $256.40  
  Purchase #6 $162.33   11.735%   $181.3794   $181.38   $181.40   $181.40  
  Purchase #7 $211.96   13.206%   $239.9514   $239.95   $239.95   $240.00  
  7 purchase totals = $1,121.61       $1,252.6621   $1,252.66   $1,252.65   $1,252.70