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 $36.35   5.621%   $38.3932   $38.39   $38.40   $38.40  
  Purchase #2 $242.51   10.785%   $268.6647   $268.66   $268.65   $268.70  
  Purchase #3 $15.71   7.642%   $16.9106   $16.91   $16.90   $16.90  
  Purchase #4 $228.93   7.148%   $245.2939   $245.29   $245.30   $245.30  
  Purchase #5 $86.47   7.831%   $93.2415   $93.24   $93.25   $93.20  
  Purchase #6 $100.69   9.580%   $110.3361   $110.34   $110.35   $110.30  
  Purchase #7 $21.91   9.764%   $24.0493   $24.05   $24.05   $24.00  
  7 purchase totals = $732.57       $796.8893   $796.88   $796.90   $796.80