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 $129.85   4.769%   $136.0425   $136.04   $136.05   $136.00  
  Purchase #2 $221.39   9.152%   $241.6516   $241.65   $241.65   $241.70  
  Purchase #3 $219.42   7.482%   $235.837   $235.84   $235.85   $235.80  
  Purchase #4 $150.29   9.689%   $164.8516   $164.85   $164.85   $164.90  
  Purchase #5 $136.30   4.223%   $142.0559   $142.06   $142.05   $142.10  
  Purchase #6 $212.37   12.197%   $238.2728   $238.27   $238.25   $238.30  
  Purchase #7 $204.90   3.657%   $212.3932   $212.39   $212.40   $212.40  
  7 purchase totals = $1,274.52       $1,371.1046   $1,371.10   $1,371.10   $1,371.20