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 $238.55   6.190%   $253.3162   $253.32   $253.30   $253.30  
  Purchase #2 $151.87   3.150%   $156.6539   $156.65   $156.65   $156.70  
  Purchase #3 $112.37   12.103%   $125.9701   $125.97   $125.95   $126.00  
  Purchase #4 $88.53   3.223%   $91.3833   $91.38   $91.40   $91.40  
  Purchase #5 $151.61   4.606%   $158.5932   $158.59   $158.60   $158.60  
  Purchase #6 $95.81   6.556%   $102.0913   $102.09   $102.10   $102.10  
  Purchase #7 $156.50   6.719%   $167.0152   $167.02   $167.00   $167.00  
  7 purchase totals = $995.24       $1,055.0232   $1,055.02   $1,055.00   $1,055.10