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 $94.91   11.871%   $106.1768   $106.18   $106.20   $106.20  
  Purchase #2 $144.73   12.380%   $162.6476   $162.65   $162.65   $162.60  
  Purchase #3 $57.45   9.531%   $62.9256   $62.93   $62.95   $62.90  
  Purchase #4 $159.57   8.866%   $173.7175   $173.72   $173.70   $173.70  
  Purchase #5 $155.90   3.164%   $160.8327   $160.83   $160.85   $160.80  
  Purchase #6 $172.38   5.779%   $182.3418   $182.34   $182.35   $182.30  
  Purchase #7 $232.72   11.654%   $259.8412   $259.84   $259.85   $259.80  
  7 purchase totals = $1,017.66       $1,108.4832   $1,108.49   $1,108.55   $1,108.30