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 $185.35   10.581%   $204.9619   $204.96   $204.95   $205.00  
  Purchase #2 $205.82   12.556%   $231.6628   $231.66   $231.65   $231.70  
  Purchase #3 $22.35   6.300%   $23.7581   $23.76   $23.75   $23.80  
  Purchase #4 $143.39   5.846%   $151.7726   $151.77   $151.75   $151.80  
  Purchase #5 $208.65   4.144%   $217.2965   $217.30   $217.30   $217.30  
  Purchase #6 $211.64   11.361%   $235.6844   $235.68   $235.70   $235.70  
  Purchase #7 $18.59   11.371%   $20.7039   $20.70   $20.70   $20.70  
  7 purchase totals = $995.79       $1,085.8402   $1,085.83   $1,085.80   $1,086.00