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 $7.50   5.408%   $7.9056   $7.91   $7.90   $7.90  
  Purchase #2 $200.70   10.651%   $222.0766   $222.08   $222.10   $222.10  
  Purchase #3 $175.75   11.211%   $195.4533   $195.45   $195.45   $195.50  
  Purchase #4 $241.25   4.304%   $251.6334   $251.63   $251.65   $251.60  
  Purchase #5 $147.98   12.868%   $167.0221   $167.02   $167.00   $167.00  
  Purchase #6 $147.91   6.319%   $157.2564   $157.26   $157.25   $157.30  
  Purchase #7 $151.30   4.841%   $158.6244   $158.62   $158.60   $158.60  
  7 purchase totals = $1,072.39       $1,159.9718   $1,159.97   $1,159.95   $1,160.00