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 $144.96   5.334%   $152.6922   $152.69   $152.70   $152.70  
  Purchase #2 $207.70   3.419%   $214.8013   $214.80   $214.80   $214.80  
  Purchase #3 $120.56   10.817%   $133.601   $133.60   $133.60   $133.60  
  Purchase #4 $65.86   13.820%   $74.9619   $74.96   $74.95   $75.00  
  Purchase #5 $198.40   9.698%   $217.6408   $217.64   $217.65   $217.60  
  Purchase #6 $92.25   3.665%   $95.631   $95.63   $95.65   $95.60  
  Purchase #7 $29.25   8.468%   $31.7269   $31.73   $31.75   $31.70  
  7 purchase totals = $858.98       $921.0551   $921.05   $921.10   $921.00