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 $39.79   8.351%   $43.1129   $43.11   $43.10   $43.10  
  Purchase #2 $235.36   13.330%   $266.7335   $266.73   $266.75   $266.70  
  Purchase #3 $57.41   11.122%   $63.7951   $63.80   $63.80   $63.80  
  Purchase #4 $95.94   8.279%   $103.8829   $103.88   $103.90   $103.90  
  Purchase #5 $171.46   11.641%   $191.4197   $191.42   $191.40   $191.40  
  Purchase #6 $113.89   6.536%   $121.3339   $121.33   $121.35   $121.30  
  Purchase #7 $215.40   7.259%   $231.0359   $231.04   $231.05   $231.00  
  7 purchase totals = $929.25       $1,021.3139   $1,021.31   $1,021.35   $1,021.20