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 $215.57   8.791%   $234.5208   $234.52   $234.50   $234.50  
  Purchase #2 $239.73   4.378%   $250.2254   $250.23   $250.25   $250.20  
  Purchase #3 $223.86   6.390%   $238.1647   $238.16   $238.15   $238.20  
  Purchase #4 $249.47   8.299%   $270.1735   $270.17   $270.15   $270.20  
  Purchase #5 $201.28   3.123%   $207.566   $207.57   $207.55   $207.60  
  Purchase #6 $143.88   11.568%   $160.524   $160.52   $160.50   $160.50  
  Purchase #7 $34.99   4.160%   $36.4456   $36.45   $36.45   $36.40  
  7 purchase totals = $1,308.78       $1,397.6200   $1,397.62   $1,397.55   $1,397.60