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 $122.47   10.731%   $135.6123   $135.61   $135.60   $135.60  
  Purchase #2 $211.89   13.538%   $240.5757   $240.58   $240.60   $240.60  
  Purchase #3 $155.90   11.406%   $173.682   $173.68   $173.70   $173.70  
  Purchase #4 $147.54   7.745%   $158.967   $158.97   $158.95   $159.00  
  Purchase #5 $203.83   4.122%   $212.2319   $212.23   $212.25   $212.20  
  Purchase #6 $119.85   4.316%   $125.0227   $125.02   $125.00   $125.00  
  Purchase #7 $11.33   6.732%   $12.0927   $12.09   $12.10   $12.10  
  7 purchase totals = $972.81       $1,058.1843   $1,058.18   $1,058.20   $1,058.20