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 $141.29   3.799%   $146.6576   $146.66   $146.65   $146.70  
  Purchase #2 $23.61   6.752%   $25.2041   $25.20   $25.20   $25.20  
  Purchase #3 $98.58   11.233%   $109.6535   $109.65   $109.65   $109.70  
  Purchase #4 $68.52   13.229%   $77.5845   $77.58   $77.60   $77.60  
  Purchase #5 $180.27   3.622%   $186.7994   $186.80   $186.80   $186.80  
  Purchase #6 $72.48   3.715%   $75.1726   $75.17   $75.15   $75.20  
  Purchase #7 $124.65   7.742%   $134.3004   $134.30   $134.30   $134.30  
  7 purchase totals = $709.40       $755.3721   $755.36   $755.35   $755.50