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 $197.96   3.391%   $204.6728   $204.67   $204.65   $204.70  
  Purchase #2 $232.31   4.153%   $241.9578   $241.96   $241.95   $242.00  
  Purchase #3 $223.57   5.144%   $235.0704   $235.07   $235.05   $235.10  
  Purchase #4 $64.93   8.750%   $70.6114   $70.61   $70.60   $70.60  
  Purchase #5 $237.76   11.613%   $265.3711   $265.37   $265.35   $265.40  
  Purchase #6 $91.95   7.506%   $98.8518   $98.85   $98.85   $98.90  
  Purchase #7 $94.76   7.120%   $101.5069   $101.51   $101.50   $101.50  
  7 purchase totals = $1,143.24       $1,218.0422   $1,218.04   $1,217.95   $1,218.20