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 $62.97   11.696%   $70.335   $70.34   $70.35   $70.30  
  Purchase #2 $121.30   10.332%   $133.8327   $133.83   $133.85   $133.80  
  Purchase #3 $110.51   6.612%   $117.8169   $117.82   $117.80   $117.80  
  Purchase #4 $218.32   7.420%   $234.5193   $234.52   $234.50   $234.50  
  Purchase #5 $47.63   12.696%   $53.6771   $53.68   $53.70   $53.70  
  Purchase #6 $175.68   10.854%   $194.7483   $194.75   $194.75   $194.70  
  Purchase #7 $191.42   7.802%   $206.3546   $206.35   $206.35   $206.40  
  7 purchase totals = $927.83       $1,011.2839   $1,011.29   $1,011.30   $1,011.20