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 $234.62   13.506%   $266.3078   $266.31   $266.30   $266.30  
  Purchase #2 $129.83   5.849%   $137.4238   $137.42   $137.40   $137.40  
  Purchase #3 $140.50   5.321%   $147.976   $147.98   $148.00   $148.00  
  Purchase #4 $194.44   3.823%   $201.8734   $201.87   $201.85   $201.90  
  Purchase #5 $13.79   11.785%   $15.4152   $15.42   $15.40   $15.40  
  Purchase #6 $219.46   11.178%   $243.9912   $243.99   $244.00   $244.00  
  Purchase #7 $36.41   3.299%   $37.6112   $37.61   $37.60   $37.60  
  7 purchase totals = $969.05       $1,050.5986   $1,050.60   $1,050.55   $1,050.60