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 $86.52   10.644%   $95.7292   $95.73   $95.75   $95.70  
  Purchase #2 $107.88   10.342%   $119.0369   $119.04   $119.05   $119.00  
  Purchase #3 $16.25   9.244%   $17.7522   $17.75   $17.75   $17.80  
  Purchase #4 $223.94   11.233%   $249.0952   $249.10   $249.10   $249.10  
  Purchase #5 $140.49   3.659%   $145.6305   $145.63   $145.65   $145.60  
  Purchase #6 $85.44   3.349%   $88.3014   $88.30   $88.30   $88.30  
  Purchase #7 $29.85   6.239%   $31.7123   $31.71   $31.70   $31.70  
  7 purchase totals = $690.37       $747.2577   $747.26   $747.30   $747.20