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 $58.63   5.441%   $61.8201   $61.82   $61.80   $61.80  
  Purchase #2 $74.63   8.770%   $81.1751   $81.18   $81.20   $81.20  
  Purchase #3 $165.33   11.219%   $183.8784   $183.88   $183.90   $183.90  
  Purchase #4 $39.83   13.692%   $45.2835   $45.28   $45.30   $45.30  
  Purchase #5 $235.28   13.614%   $267.311   $267.31   $267.30   $267.30  
  Purchase #6 $34.54   4.292%   $36.0225   $36.02   $36.00   $36.00  
  Purchase #7 $78.61   12.662%   $88.5636   $88.56   $88.55   $88.60  
  7 purchase totals = $686.85       $764.0542   $764.05   $764.05   $764.10