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 $183.85   9.795%   $201.8581   $201.86   $201.85   $201.90  
  Purchase #2 $19.39   10.745%   $21.4735   $21.47   $21.45   $21.50  
  Purchase #3 $108.64   13.667%   $123.4878   $123.49   $123.50   $123.50  
  Purchase #4 $167.57   8.374%   $181.6023   $181.60   $181.60   $181.60  
  Purchase #5 $154.25   5.831%   $163.2443   $163.24   $163.25   $163.20  
  Purchase #6 $162.62   11.477%   $181.2839   $181.28   $181.30   $181.30  
  Purchase #7 $236.92   3.136%   $244.3498   $244.35   $244.35   $244.30  
  7 purchase totals = $1,033.24       $1,117.2997   $1,117.29   $1,117.30   $1,117.30