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 $34.87   5.476%   $36.7795   $36.78   $36.80   $36.80  
  Purchase #2 $102.82   10.545%   $113.6624   $113.66   $113.65   $113.70  
  Purchase #3 $205.71   9.824%   $225.919   $225.92   $225.90   $225.90  
  Purchase #4 $245.50   7.235%   $263.2619   $263.26   $263.25   $263.30  
  Purchase #5 $247.47   11.700%   $276.424   $276.42   $276.40   $276.40  
  Purchase #6 $247.89   3.797%   $257.3024   $257.30   $257.30   $257.30  
  Purchase #7 $185.85   8.370%   $201.4056   $201.41   $201.40   $201.40  
  7 purchase totals = $1,270.11       $1,374.7548   $1,374.75   $1,374.70   $1,374.80