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 $10.61   6.869%   $11.3388   $11.34   $11.35   $11.30  
  Purchase #2 $181.97   7.833%   $196.2237   $196.22   $196.20   $196.20  
  Purchase #3 $194.59   4.714%   $203.763   $203.76   $203.75   $203.80  
  Purchase #4 $147.75   4.214%   $153.9762   $153.98   $154.00   $154.00  
  Purchase #5 $191.29   4.786%   $200.4451   $200.45   $200.45   $200.40  
  Purchase #6 $14.87   7.229%   $15.945   $15.95   $15.95   $15.90  
  Purchase #7 $156.58   11.872%   $175.1692   $175.17   $175.15   $175.20  
  7 purchase totals = $897.66       $956.8610   $956.87   $956.85   $956.80