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 $129.75   3.563%   $134.373   $134.37   $134.35   $134.40  
  Purchase #2 $229.88   10.763%   $254.622   $254.62   $254.60   $254.60  
  Purchase #3 $195.96   11.618%   $218.7266   $218.73   $218.75   $218.70  
  Purchase #4 $76.32   4.440%   $79.7086   $79.71   $79.70   $79.70  
  Purchase #5 $163.54   6.757%   $174.5904   $174.59   $174.60   $174.60  
  Purchase #6 $67.45   12.492%   $75.8759   $75.88   $75.90   $75.90  
  Purchase #7 $161.65   9.499%   $177.0051   $177.01   $177.00   $177.00  
  7 purchase totals = $1,024.55       $1,114.9016   $1,114.91   $1,114.90   $1,114.90