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 $218.76   11.329%   $243.5433   $243.54   $243.55   $243.50  
  Purchase #2 $150.31   9.155%   $164.0709   $164.07   $164.05   $164.10  
  Purchase #3 $59.28   3.765%   $61.5119   $61.51   $61.50   $61.50  
  Purchase #4 $159.71   5.218%   $168.0437   $168.04   $168.05   $168.00  
  Purchase #5 $46.99   6.362%   $49.9795   $49.98   $50.00   $50.00  
  Purchase #6 $96.39   10.643%   $106.6488   $106.65   $106.65   $106.60  
  Purchase #7 $174.73   13.322%   $198.0075   $198.01   $198.00   $198.00  
  7 purchase totals = $906.17       $991.8056   $991.80   $991.80   $991.70