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 $127.70   10.416%   $141.0012   $141.00   $141.00   $141.00  
  Purchase #2 $218.79   13.191%   $247.6506   $247.65   $247.65   $247.70  
  Purchase #3 $119.88   9.312%   $131.0432   $131.04   $131.05   $131.00  
  Purchase #4 $110.84   12.589%   $124.7936   $124.79   $124.80   $124.80  
  Purchase #5 $207.79   13.442%   $235.7211   $235.72   $235.70   $235.70  
  Purchase #6 $65.58   10.766%   $72.6403   $72.64   $72.65   $72.60  
  Purchase #7 $182.93   9.866%   $200.9779   $200.98   $201.00   $201.00  
  7 purchase totals = $1,033.51       $1,153.8279   $1,153.82   $1,153.85   $1,153.80