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 $49.87   13.460%   $56.5825   $56.58   $56.60   $56.60  
  Purchase #2 $177.72   11.392%   $197.9659   $197.97   $197.95   $198.00  
  Purchase #3 $77.70   13.312%   $88.0434   $88.04   $88.05   $88.00  
  Purchase #4 $121.75   12.783%   $137.3133   $137.31   $137.30   $137.30  
  Purchase #5 $11.29   6.206%   $11.9907   $11.99   $12.00   $12.00  
  Purchase #6 $158.42   5.414%   $166.9969   $167.00   $167.00   $167.00  
  Purchase #7 $153.98   7.811%   $166.0074   $166.01   $166.00   $166.00  
  7 purchase totals = $750.73       $824.9001   $824.90   $824.90   $824.90