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 $55.74   6.256%   $59.2271   $59.23   $59.25   $59.20  
  Purchase #2 $153.26   5.730%   $162.0418   $162.04   $162.05   $162.00  
  Purchase #3 $175.65   12.213%   $197.1021   $197.10   $197.10   $197.10  
  Purchase #4 $220.87   11.296%   $245.8195   $245.82   $245.80   $245.80  
  Purchase #5 $58.91   8.644%   $64.0022   $64.00   $64.00   $64.00  
  Purchase #6 $222.28   5.381%   $234.2409   $234.24   $234.25   $234.20  
  Purchase #7 $228.29   4.650%   $238.9055   $238.91   $238.90   $238.90  
  7 purchase totals = $1,115.00       $1,201.3391   $1,201.34   $1,201.35   $1,201.20