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 $58.45   13.658%   $66.4331   $66.43   $66.45   $66.40  
  Purchase #2 $229.34   13.217%   $259.6519   $259.65   $259.65   $259.70  
  Purchase #3 $200.51   4.198%   $208.9274   $208.93   $208.95   $208.90  
  Purchase #4 $20.86   6.589%   $22.2345   $22.23   $22.25   $22.20  
  Purchase #5 $157.43   10.866%   $174.5363   $174.54   $174.55   $174.50  
  Purchase #6 $242.73   5.674%   $256.5025   $256.50   $256.50   $256.50  
  Purchase #7 $167.64   8.479%   $181.8542   $181.85   $181.85   $181.90  
  7 purchase totals = $1,076.96       $1,170.1399   $1,170.13   $1,170.20   $1,170.10