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 $161.42   8.177%   $174.6193   $174.62   $174.60   $174.60  
  Purchase #2 $230.59   10.453%   $254.6936   $254.69   $254.70   $254.70  
  Purchase #3 $121.56   13.814%   $138.3523   $138.35   $138.35   $138.40  
  Purchase #4 $191.55   13.761%   $217.9092   $217.91   $217.90   $217.90  
  Purchase #5 $17.90   6.412%   $19.0477   $19.05   $19.05   $19.00  
  Purchase #6 $95.31   10.176%   $105.0087   $105.01   $105.00   $105.00  
  Purchase #7 $99.76   13.414%   $113.1418   $113.14   $113.15   $113.10  
  7 purchase totals = $918.09       $1,022.7726   $1,022.77   $1,022.75   $1,022.70