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 $48.64   10.530%   $53.7618   $53.76   $53.75   $53.80  
  Purchase #2 $192.71   8.474%   $209.0402   $209.04   $209.05   $209.00  
  Purchase #3 $37.60   5.552%   $39.6876   $39.69   $39.70   $39.70  
  Purchase #4 $149.85   8.448%   $162.5093   $162.51   $162.50   $162.50  
  Purchase #5 $140.30   5.665%   $148.248   $148.25   $148.25   $148.20  
  Purchase #6 $213.31   5.854%   $225.7972   $225.80   $225.80   $225.80  
  Purchase #7 $177.67   5.585%   $187.5929   $187.59   $187.60   $187.60  
  7 purchase totals = $960.08       $1,026.6370   $1,026.64   $1,026.65   $1,026.60