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 $62.67   13.824%   $71.3335   $71.33   $71.35   $71.30  
  Purchase #2 $29.32   13.269%   $33.2105   $33.21   $33.20   $33.20  
  Purchase #3 $59.94   3.281%   $61.9066   $61.91   $61.90   $61.90  
  Purchase #4 $241.71   4.374%   $252.2824   $252.28   $252.30   $252.30  
  Purchase #5 $92.71   12.802%   $104.5787   $104.58   $104.60   $104.60  
  Purchase #6 $149.97   7.315%   $160.9403   $160.94   $160.95   $160.90  
  Purchase #7 $216.70   10.558%   $239.5792   $239.58   $239.60   $239.60  
  7 purchase totals = $853.02       $923.8312   $923.83   $923.90   $923.80