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 $212.71   13.698%   $241.847   $241.85   $241.85   $241.80  
  Purchase #2 $8.37   8.116%   $9.0493   $9.05   $9.05   $9.00  
  Purchase #3 $16.85   6.863%   $18.0064   $18.01   $18.00   $18.00  
  Purchase #4 $161.65   8.560%   $175.4872   $175.49   $175.50   $175.50  
  Purchase #5 $123.28   6.132%   $130.8395   $130.84   $130.85   $130.80  
  Purchase #6 $203.78   4.311%   $212.565   $212.57   $212.55   $212.60  
  Purchase #7 $14.64   4.315%   $15.2717   $15.27   $15.25   $15.30  
  7 purchase totals = $741.28       $803.0661   $803.08   $803.05   $803.00