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 $70.33   6.585%   $74.9612   $74.96   $74.95   $75.00  
  Purchase #2 $180.96   3.392%   $187.0982   $187.10   $187.10   $187.10  
  Purchase #3 $56.94   6.702%   $60.7561   $60.76   $60.75   $60.80  
  Purchase #4 $9.76   8.364%   $10.5763   $10.58   $10.60   $10.60  
  Purchase #5 $171.81   9.831%   $188.7006   $188.70   $188.70   $188.70  
  Purchase #6 $234.50   9.132%   $255.9145   $255.91   $255.90   $255.90  
  Purchase #7 $45.39   4.111%   $47.256   $47.26   $47.25   $47.30  
  7 purchase totals = $769.69       $825.2629   $825.27   $825.25   $825.40