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 $174.84   9.432%   $191.3309   $191.33   $191.35   $191.30  
  Purchase #2 $59.97   8.391%   $65.0021   $65.00   $65.00   $65.00  
  Purchase #3 $245.37   7.461%   $263.6771   $263.68   $263.70   $263.70  
  Purchase #4 $29.29   8.162%   $31.6806   $31.68   $31.70   $31.70  
  Purchase #5 $93.55   3.111%   $96.4603   $96.46   $96.45   $96.50  
  Purchase #6 $43.78   3.285%   $45.2182   $45.22   $45.20   $45.20  
  Purchase #7 $124.77   9.112%   $136.139   $136.14   $136.15   $136.10  
  7 purchase totals = $771.57       $829.5082   $829.51   $829.55   $829.50