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 $142.79   10.117%   $157.2361   $157.24   $157.25   $157.20  
  Purchase #2 $184.71   4.788%   $193.5539   $193.55   $193.55   $193.60  
  Purchase #3 $92.99   9.248%   $101.5897   $101.59   $101.60   $101.60  
  Purchase #4 $245.53   3.188%   $253.3575   $253.36   $253.35   $253.40  
  Purchase #5 $64.72   5.796%   $68.4712   $68.47   $68.45   $68.50  
  Purchase #6 $188.26   4.386%   $196.5171   $196.52   $196.50   $196.50  
  Purchase #7 $56.36   12.493%   $63.4011   $63.40   $63.40   $63.40  
  7 purchase totals = $975.36       $1,034.1266   $1,034.13   $1,034.10   $1,034.20