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 $71.75   11.558%   $80.0429   $80.04   $80.05   $80.00  
  Purchase #2 $130.98   13.633%   $148.8365   $148.84   $148.85   $148.80  
  Purchase #3 $48.98   6.302%   $52.0667   $52.07   $52.05   $52.10  
  Purchase #4 $241.58   5.514%   $254.9007   $254.90   $254.90   $254.90  
  Purchase #5 $41.84   12.797%   $47.1943   $47.19   $47.20   $47.20  
  Purchase #6 $214.94   8.456%   $233.1153   $233.12   $233.10   $233.10  
  Purchase #7 $218.62   8.213%   $236.5753   $236.58   $236.60   $236.60  
  7 purchase totals = $968.69       $1,052.7317   $1,052.74   $1,052.75   $1,052.70