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 $195.41   11.618%   $218.1127   $218.11   $218.10   $218.10  
  Purchase #2 $229.81   13.521%   $260.8826   $260.88   $260.90   $260.90  
  Purchase #3 $59.27   4.148%   $61.7285   $61.73   $61.75   $61.70  
  Purchase #4 $167.57   13.210%   $189.706   $189.71   $189.70   $189.70  
  Purchase #5 $96.46   12.183%   $108.2117   $108.21   $108.20   $108.20  
  Purchase #6 $86.42   12.835%   $97.512   $97.51   $97.50   $97.50  
  Purchase #7 $106.82   10.632%   $118.1771   $118.18   $118.20   $118.20  
  7 purchase totals = $941.76       $1,054.3306   $1,054.33   $1,054.35   $1,054.30