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 $184.47   8.397%   $199.9599   $199.96   $199.95   $200.00  
  Purchase #2 $31.82   3.231%   $32.8481   $32.85   $32.85   $32.80  
  Purchase #3 $109.74   8.295%   $118.8429   $118.84   $118.85   $118.80  
  Purchase #4 $39.78   11.113%   $44.2008   $44.20   $44.20   $44.20  
  Purchase #5 $165.32   10.257%   $182.2769   $182.28   $182.30   $182.30  
  Purchase #6 $73.28   12.816%   $82.6716   $82.67   $82.65   $82.70  
  Purchase #7 $83.26   6.444%   $88.6253   $88.63   $88.65   $88.60  
  7 purchase totals = $687.67       $749.4255   $749.43   $749.45   $749.40