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 $241.25   5.222%   $253.8481   $253.85   $253.85   $253.80  
  Purchase #2 $45.74   8.148%   $49.4669   $49.47   $49.45   $49.50  
  Purchase #3 $99.50   12.337%   $111.7753   $111.78   $111.80   $111.80  
  Purchase #4 $227.57   9.540%   $249.2802   $249.28   $249.30   $249.30  
  Purchase #5 $43.43   8.393%   $47.0751   $47.08   $47.10   $47.10  
  Purchase #6 $197.98   10.295%   $218.362   $218.36   $218.35   $218.40  
  Purchase #7 $31.29   12.396%   $35.1687   $35.17   $35.15   $35.20  
  7 purchase totals = $886.76       $964.9763   $964.99   $965.00   $965.10