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 $217.64   12.144%   $244.0702   $244.07   $244.05   $244.10  
  Purchase #2 $88.68   6.712%   $94.6322   $94.63   $94.65   $94.60  
  Purchase #3 $227.94   8.549%   $247.4266   $247.43   $247.45   $247.40  
  Purchase #4 $172.98   13.861%   $196.9568   $196.96   $196.95   $197.00  
  Purchase #5 $168.31   11.721%   $188.0376   $188.04   $188.05   $188.00  
  Purchase #6 $209.85   11.827%   $234.669   $234.67   $234.65   $234.70  
  Purchase #7 $87.73   4.600%   $91.7656   $91.77   $91.75   $91.80  
  7 purchase totals = $1,173.13       $1,297.5580   $1,297.57   $1,297.55   $1,297.60