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 $202.83   11.770%   $226.7031   $226.70   $226.70   $226.70  
  Purchase #2 $222.93   13.655%   $253.3711   $253.37   $253.35   $253.40  
  Purchase #3 $226.37   12.114%   $253.7925   $253.79   $253.80   $253.80  
  Purchase #4 $189.98   5.529%   $200.484   $200.48   $200.50   $200.50  
  Purchase #5 $31.34   3.763%   $32.5193   $32.52   $32.50   $32.50  
  Purchase #6 $15.71   8.568%   $17.056   $17.06   $17.05   $17.10  
  Purchase #7 $67.78   12.293%   $76.1122   $76.11   $76.10   $76.10  
  7 purchase totals = $956.94       $1,060.0382   $1,060.03   $1,060.00   $1,060.10