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 $217.75   13.312%   $246.7369   $246.74   $246.75   $246.70  
  Purchase #2 $200.73   5.540%   $211.8504   $211.85   $211.85   $211.90  
  Purchase #3 $79.98   6.183%   $84.9252   $84.93   $84.95   $84.90  
  Purchase #4 $58.74   4.651%   $61.472   $61.47   $61.45   $61.50  
  Purchase #5 $186.78   6.708%   $199.3092   $199.31   $199.30   $199.30  
  Purchase #6 $45.88   9.464%   $50.2221   $50.22   $50.20   $50.20  
  Purchase #7 $180.44   13.850%   $205.4309   $205.43   $205.45   $205.40  
  7 purchase totals = $970.30       $1,059.9467   $1,059.95   $1,059.95   $1,059.90