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 $241.70   8.772%   $262.9019   $262.90   $262.90   $262.90  
  Purchase #2 $246.30   11.662%   $275.0235   $275.02   $275.00   $275.00  
  Purchase #3 $44.38   11.523%   $49.4939   $49.49   $49.50   $49.50  
  Purchase #4 $52.98   6.375%   $56.3575   $56.36   $56.35   $56.40  
  Purchase #5 $171.96   5.451%   $181.3335   $181.33   $181.35   $181.30  
  Purchase #6 $229.28   3.249%   $236.7293   $236.73   $236.75   $236.70  
  Purchase #7 $140.36   5.428%   $147.9787   $147.98   $148.00   $148.00  
  7 purchase totals = $1,126.96       $1,209.8183   $1,209.81   $1,209.85   $1,209.80