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 $127.27   7.534%   $136.8585   $136.86   $136.85   $136.90  
  Purchase #2 $216.94   11.865%   $242.6799   $242.68   $242.70   $242.70  
  Purchase #3 $230.59   3.185%   $237.9343   $237.93   $237.95   $237.90  
  Purchase #4 $38.28   7.797%   $41.2647   $41.26   $41.25   $41.30  
  Purchase #5 $186.43   9.616%   $204.3571   $204.36   $204.35   $204.40  
  Purchase #6 $159.28   5.135%   $167.459   $167.46   $167.45   $167.50  
  Purchase #7 $58.40   7.663%   $62.8752   $62.88   $62.90   $62.90  
  7 purchase totals = $1,017.19       $1,093.4287   $1,093.43   $1,093.45   $1,093.60