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 $195.36   13.311%   $221.3644   $221.36   $221.35   $221.40  
  Purchase #2 $106.89   11.639%   $119.3309   $119.33   $119.35   $119.30  
  Purchase #3 $86.92   6.433%   $92.5116   $92.51   $92.50   $92.50  
  Purchase #4 $50.68   6.759%   $54.1055   $54.11   $54.10   $54.10  
  Purchase #5 $195.64   3.793%   $203.0606   $203.06   $203.05   $203.10  
  Purchase #6 $179.58   9.530%   $196.694   $196.69   $196.70   $196.70  
  Purchase #7 $99.60   8.746%   $108.311   $108.31   $108.30   $108.30  
  7 purchase totals = $914.67       $995.3780   $995.37   $995.35   $995.40