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 $223.56   13.283%   $253.2555   $253.26   $253.25   $253.30  
  Purchase #2 $195.78   11.394%   $218.0872   $218.09   $218.10   $218.10  
  Purchase #3 $57.71   6.129%   $61.247   $61.25   $61.25   $61.20  
  Purchase #4 $182.33   12.623%   $205.3455   $205.35   $205.35   $205.30  
  Purchase #5 $31.66   9.854%   $34.7798   $34.78   $34.80   $34.80  
  Purchase #6 $60.36   6.785%   $64.4554   $64.46   $64.45   $64.50  
  Purchase #7 $195.79   11.465%   $218.2373   $218.24   $218.25   $218.20  
  7 purchase totals = $947.19       $1,055.4077   $1,055.43   $1,055.45   $1,055.40