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 $67.38   13.787%   $76.6697   $76.67   $76.65   $76.70  
  Purchase #2 $211.92   11.446%   $236.1764   $236.18   $236.20   $236.20  
  Purchase #3 $55.28   4.823%   $57.9462   $57.95   $57.95   $57.90  
  Purchase #4 $203.79   12.842%   $229.9607   $229.96   $229.95   $230.00  
  Purchase #5 $13.74   12.614%   $15.4732   $15.47   $15.45   $15.50  
  Purchase #6 $202.74   8.737%   $220.4534   $220.45   $220.45   $220.50  
  Purchase #7 $22.43   5.444%   $23.6511   $23.65   $23.65   $23.70  
  7 purchase totals = $777.28       $860.3307   $860.33   $860.30   $860.50