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 $196.88   5.582%   $207.8698   $207.87   $207.85   $207.90  
  Purchase #2 $67.36   12.251%   $75.6123   $75.61   $75.60   $75.60  
  Purchase #3 $147.99   8.729%   $160.908   $160.91   $160.90   $160.90  
  Purchase #4 $90.96   7.141%   $97.4555   $97.46   $97.45   $97.50  
  Purchase #5 $178.87   12.446%   $201.1322   $201.13   $201.15   $201.10  
  Purchase #6 $5.97   5.527%   $6.3   $6.30   $6.30   $6.30  
  Purchase #7 $32.76   6.594%   $34.9202   $34.92   $34.90   $34.90  
  7 purchase totals = $720.79       $784.1980   $784.20   $784.15   $784.20