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 $247.78   5.832%   $262.2305   $262.23   $262.25   $262.20  
  Purchase #2 $34.28   6.862%   $36.6323   $36.63   $36.65   $36.60  
  Purchase #3 $66.65   7.618%   $71.7274   $71.73   $71.75   $71.70  
  Purchase #4 $56.98   10.602%   $63.021   $63.02   $63.00   $63.00  
  Purchase #5 $241.60   7.461%   $259.6258   $259.63   $259.65   $259.60  
  Purchase #6 $209.30   3.584%   $216.8013   $216.80   $216.80   $216.80  
  Purchase #7 $101.40   7.435%   $108.9391   $108.94   $108.95   $108.90  
  7 purchase totals = $957.99       $1,018.9774   $1,018.98   $1,019.05   $1,018.80