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 $197.98   13.795%   $225.2913   $225.29   $225.30   $225.30  
  Purchase #2 $177.53   11.640%   $198.1945   $198.19   $198.20   $198.20  
  Purchase #3 $85.36   9.466%   $93.4402   $93.44   $93.45   $93.40  
  Purchase #4 $93.36   13.609%   $106.0654   $106.07   $106.05   $106.10  
  Purchase #5 $160.88   6.451%   $171.2584   $171.26   $171.25   $171.30  
  Purchase #6 $155.52   7.435%   $167.0829   $167.08   $167.10   $167.10  
  Purchase #7 $22.63   5.487%   $23.8717   $23.87   $23.85   $23.90  
  7 purchase totals = $893.26       $985.2044   $985.20   $985.20   $985.30