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 $47.39   11.501%   $52.8403   $52.84   $52.85   $52.80  
  Purchase #2 $218.85   9.191%   $238.9645   $238.96   $238.95   $239.00  
  Purchase #3 $231.33   12.651%   $260.5956   $260.60   $260.60   $260.60  
  Purchase #4 $249.36   8.697%   $271.0468   $271.05   $271.05   $271.00  
  Purchase #5 $162.31   11.694%   $181.2905   $181.29   $181.30   $181.30  
  Purchase #6 $20.27   3.237%   $20.9261   $20.93   $20.95   $20.90  
  Purchase #7 $217.68   11.168%   $241.9905   $241.99   $242.00   $242.00  
  7 purchase totals = $1,147.19       $1,267.6543   $1,267.66   $1,267.70   $1,267.60