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 $84.97   9.743%   $93.2486   $93.25   $93.25   $93.20  
  Purchase #2 $23.34   12.171%   $26.1807   $26.18   $26.20   $26.20  
  Purchase #3 $203.64   12.414%   $228.9199   $228.92   $228.90   $228.90  
  Purchase #4 $245.37   7.622%   $264.0721   $264.07   $264.05   $264.10  
  Purchase #5 $133.49   9.130%   $145.6776   $145.68   $145.70   $145.70  
  Purchase #6 $170.56   9.224%   $186.2925   $186.29   $186.30   $186.30  
  Purchase #7 $56.37   3.798%   $58.5109   $58.51   $58.50   $58.50  
  7 purchase totals = $917.74       $1,002.9023   $1,002.90   $1,002.90   $1,002.90