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 $142.95   7.699%   $153.9557   $153.96   $153.95   $154.00  
  Purchase #2 $90.25   7.434%   $96.9592   $96.96   $96.95   $97.00  
  Purchase #3 $44.90   10.385%   $49.5629   $49.56   $49.55   $49.60  
  Purchase #4 $240.42   3.871%   $249.7267   $249.73   $249.75   $249.70  
  Purchase #5 $100.82   4.417%   $105.2732   $105.27   $105.25   $105.30  
  Purchase #6 $127.29   6.575%   $135.6593   $135.66   $135.65   $135.70  
  Purchase #7 $36.35   7.589%   $39.1086   $39.11   $39.10   $39.10  
  7 purchase totals = $782.98       $830.2456   $830.25   $830.20   $830.40