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 $205.93   9.577%   $225.6519   $225.65   $225.65   $225.70  
  Purchase #2 $51.85   13.746%   $58.9773   $58.98   $59.00   $59.00  
  Purchase #3 $215.79   13.500%   $244.9217   $244.92   $244.90   $244.90  
  Purchase #4 $157.65   5.539%   $166.3822   $166.38   $166.40   $166.40  
  Purchase #5 $56.40   13.610%   $64.076   $64.08   $64.10   $64.10  
  Purchase #6 $7.93   12.189%   $8.8966   $8.90   $8.90   $8.90  
  Purchase #7 $234.69   11.716%   $262.1863   $262.19   $262.20   $262.20  
  7 purchase totals = $930.24       $1,031.0920   $1,031.10   $1,031.15   $1,031.20