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 $88.46   6.108%   $93.8631   $93.86   $93.85   $93.90  
  Purchase #2 $213.31   4.492%   $222.8919   $222.89   $222.90   $222.90  
  Purchase #3 $197.88   11.132%   $219.908   $219.91   $219.90   $219.90  
  Purchase #4 $232.33   3.530%   $240.5312   $240.53   $240.55   $240.50  
  Purchase #5 $65.55   13.748%   $74.5618   $74.56   $74.55   $74.60  
  Purchase #6 $239.54   11.410%   $266.8715   $266.87   $266.85   $266.90  
  Purchase #7 $205.90   7.688%   $221.7296   $221.73   $221.75   $221.70  
  7 purchase totals = $1,242.97       $1,340.3571   $1,340.35   $1,340.35   $1,340.40