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 $60.87   12.856%   $68.6954   $68.70   $68.70   $68.70  
  Purchase #2 $150.40   11.445%   $167.6133   $167.61   $167.60   $167.60  
  Purchase #3 $148.77   11.672%   $166.1344   $166.13   $166.15   $166.10  
  Purchase #4 $200.45   11.463%   $223.4276   $223.43   $223.45   $223.40  
  Purchase #5 $23.91   4.194%   $24.9128   $24.91   $24.90   $24.90  
  Purchase #6 $154.88   12.742%   $174.6148   $174.61   $174.60   $174.60  
  Purchase #7 $92.81   3.380%   $95.947   $95.95   $95.95   $95.90  
  7 purchase totals = $832.09       $921.3453   $921.34   $921.35   $921.20