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 $235.70   7.476%   $253.3209   $253.32   $253.30   $253.30  
  Purchase #2 $32.89   11.703%   $36.7391   $36.74   $36.75   $36.70  
  Purchase #3 $53.90   7.424%   $57.9015   $57.90   $57.90   $57.90  
  Purchase #4 $188.77   9.286%   $206.2992   $206.30   $206.30   $206.30  
  Purchase #5 $204.89   12.557%   $230.618   $230.62   $230.60   $230.60  
  Purchase #6 $240.75   12.413%   $270.6343   $270.63   $270.65   $270.60  
  Purchase #7 $191.99   7.709%   $206.7905   $206.79   $206.80   $206.80  
  7 purchase totals = $1,148.89       $1,262.3035   $1,262.30   $1,262.30   $1,262.20