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 $178.62   9.349%   $195.3192   $195.32   $195.30   $195.30  
  Purchase #2 $60.47   7.184%   $64.8142   $64.81   $64.80   $64.80  
  Purchase #3 $245.79   12.238%   $275.8698   $275.87   $275.85   $275.90  
  Purchase #4 $219.74   6.651%   $234.3549   $234.35   $234.35   $234.40  
  Purchase #5 $25.76   7.114%   $27.5926   $27.59   $27.60   $27.60  
  Purchase #6 $63.25   10.286%   $69.7559   $69.76   $69.75   $69.80  
  Purchase #7 $110.32   6.390%   $117.3694   $117.37   $117.35   $117.40  
  7 purchase totals = $903.95       $985.0760   $985.07   $985.00   $985.20