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 $136.42   9.440%   $149.298   $149.30   $149.30   $149.30  
  Purchase #2 $106.73   11.279%   $118.7681   $118.77   $118.75   $118.80  
  Purchase #3 $227.89   13.151%   $257.8598   $257.86   $257.85   $257.90  
  Purchase #4 $150.38   6.823%   $160.6404   $160.64   $160.65   $160.60  
  Purchase #5 $204.89   5.665%   $216.497   $216.50   $216.50   $216.50  
  Purchase #6 $81.47   12.831%   $91.9234   $91.92   $91.90   $91.90  
  Purchase #7 $91.37   8.284%   $98.9391   $98.94   $98.95   $98.90  
  7 purchase totals = $999.15       $1,093.9258   $1,093.93   $1,093.90   $1,093.90