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 $85.79   8.547%   $93.1225   $93.12   $93.10   $93.10  
  Purchase #2 $220.49   10.147%   $242.8631   $242.86   $242.85   $242.90  
  Purchase #3 $187.29   3.444%   $193.7403   $193.74   $193.75   $193.70  
  Purchase #4 $78.35   6.717%   $83.6128   $83.61   $83.60   $83.60  
  Purchase #5 $43.45   4.335%   $45.3336   $45.33   $45.35   $45.30  
  Purchase #6 $133.94   9.608%   $146.809   $146.81   $146.80   $146.80  
  Purchase #7 $185.32   12.729%   $208.9094   $208.91   $208.90   $208.90  
  7 purchase totals = $934.63       $1,014.3907   $1,014.38   $1,014.35   $1,014.30