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 $213.63   8.729%   $232.2778   $232.28   $232.30   $232.30  
  Purchase #2 $104.71   6.194%   $111.1957   $111.20   $111.20   $111.20  
  Purchase #3 $161.88   8.551%   $175.7224   $175.72   $175.70   $175.70  
  Purchase #4 $147.91   13.585%   $168.0036   $168.00   $168.00   $168.00  
  Purchase #5 $120.53   12.227%   $135.2672   $135.27   $135.25   $135.30  
  Purchase #6 $167.33   10.733%   $185.2895   $185.29   $185.30   $185.30  
  Purchase #7 $50.50   9.805%   $55.4515   $55.45   $55.45   $55.50  
  7 purchase totals = $966.49       $1,063.2077   $1,063.21   $1,063.20   $1,063.30