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 $52.77   11.663%   $58.9246   $58.92   $58.90   $58.90  
  Purchase #2 $12.48   13.502%   $14.165   $14.17   $14.15   $14.20  
  Purchase #3 $187.94   10.489%   $207.653   $207.65   $207.65   $207.70  
  Purchase #4 $160.66   9.567%   $176.0303   $176.03   $176.05   $176.00  
  Purchase #5 $95.92   8.824%   $104.384   $104.38   $104.40   $104.40  
  Purchase #6 $105.75   5.171%   $111.2183   $111.22   $111.20   $111.20  
  Purchase #7 $129.78   12.329%   $145.7806   $145.78   $145.80   $145.80  
  7 purchase totals = $745.30       $818.1558   $818.15   $818.15   $818.20