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 $234.76   8.201%   $254.0127   $254.01   $254.00   $254.00  
  Purchase #2 $71.69   6.417%   $76.2903   $76.29   $76.30   $76.30  
  Purchase #3 $130.78   5.103%   $137.4537   $137.45   $137.45   $137.50  
  Purchase #4 $195.66   3.417%   $202.3457   $202.35   $202.35   $202.30  
  Purchase #5 $197.97   13.600%   $224.8939   $224.89   $224.90   $224.90  
  Purchase #6 $97.65   9.146%   $106.5811   $106.58   $106.60   $106.60  
  Purchase #7 $237.27   12.347%   $266.5657   $266.57   $266.55   $266.60  
  7 purchase totals = $1,165.78       $1,268.1431   $1,268.14   $1,268.15   $1,268.20