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 $226.55   13.705%   $257.5987   $257.60   $257.60   $257.60  
  Purchase #2 $64.62   12.745%   $72.8558   $72.86   $72.85   $72.90  
  Purchase #3 $200.44   12.624%   $225.7435   $225.74   $225.75   $225.70  
  Purchase #4 $102.47   5.119%   $107.7154   $107.72   $107.70   $107.70  
  Purchase #5 $62.52   10.304%   $68.9621   $68.96   $68.95   $69.00  
  Purchase #6 $185.46   8.306%   $200.8643   $200.86   $200.85   $200.90  
  Purchase #7 $120.47   10.330%   $132.9146   $132.91   $132.90   $132.90  
  7 purchase totals = $962.53       $1,066.6544   $1,066.65   $1,066.60   $1,066.70