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 $168.80   10.751%   $186.9477   $186.95   $186.95   $186.90  
  Purchase #2 $142.70   13.457%   $161.9031   $161.90   $161.90   $161.90  
  Purchase #3 $96.86   9.626%   $106.1837   $106.18   $106.20   $106.20  
  Purchase #4 $218.48   7.377%   $234.5973   $234.60   $234.60   $234.60  
  Purchase #5 $126.94   11.260%   $141.2334   $141.23   $141.25   $141.20  
  Purchase #6 $238.65   6.653%   $254.5274   $254.53   $254.55   $254.50  
  Purchase #7 $161.97   5.286%   $170.5317   $170.53   $170.55   $170.50  
  7 purchase totals = $1,154.40       $1,255.9243   $1,255.92   $1,256.00   $1,255.80