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 $31.84   13.460%   $36.1257   $36.13   $36.15   $36.10  
  Purchase #2 $216.43   12.289%   $243.0271   $243.03   $243.05   $243.00  
  Purchase #3 $44.90   3.454%   $46.4508   $46.45   $46.45   $46.50  
  Purchase #4 $218.69   11.208%   $243.2008   $243.20   $243.20   $243.20  
  Purchase #5 $120.43   5.137%   $126.6165   $126.62   $126.60   $126.60  
  Purchase #6 $101.47   13.746%   $115.4181   $115.42   $115.40   $115.40  
  Purchase #7 $30.49   13.524%   $34.6135   $34.61   $34.60   $34.60  
  7 purchase totals = $764.25       $845.4525   $845.46   $845.45   $845.40