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 $203.99   9.573%   $223.518   $223.52   $223.50   $223.50  
  Purchase #2 $243.94   7.645%   $262.5892   $262.59   $262.60   $262.60  
  Purchase #3 $115.72   8.842%   $125.952   $125.95   $125.95   $126.00  
  Purchase #4 $82.53   13.609%   $93.7615   $93.76   $93.75   $93.80  
  Purchase #5 $17.82   11.785%   $19.9201   $19.92   $19.90   $19.90  
  Purchase #6 $128.79   11.247%   $143.275   $143.28   $143.30   $143.30  
  Purchase #7 $175.89   10.713%   $194.7331   $194.73   $194.75   $194.70  
  7 purchase totals = $968.68       $1,063.7489   $1,063.75   $1,063.75   $1,063.80