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 $54.56   12.210%   $61.2218   $61.22   $61.20   $61.20  
  Purchase #2 $233.69   8.462%   $253.4648   $253.46   $253.45   $253.50  
  Purchase #3 $240.76   9.570%   $263.8007   $263.80   $263.80   $263.80  
  Purchase #4 $188.96   6.507%   $201.2556   $201.26   $201.25   $201.30  
  Purchase #5 $82.87   11.287%   $92.2235   $92.22   $92.20   $92.20  
  Purchase #6 $212.84   8.633%   $231.2145   $231.21   $231.20   $231.20  
  Purchase #7 $124.72   8.868%   $135.7802   $135.78   $135.80   $135.80  
  7 purchase totals = $1,138.40       $1,238.9611   $1,238.95   $1,238.90   $1,239.00