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 $124.37   8.268%   $134.6529   $134.65   $134.65   $134.70  
  Purchase #2 $249.70   12.262%   $280.3182   $280.32   $280.30   $280.30  
  Purchase #3 $120.31   8.226%   $130.2067   $130.21   $130.20   $130.20  
  Purchase #4 $35.93   10.333%   $39.6426   $39.64   $39.65   $39.60  
  Purchase #5 $187.85   10.407%   $207.3995   $207.40   $207.40   $207.40  
  Purchase #6 $56.90   5.784%   $60.1911   $60.19   $60.20   $60.20  
  Purchase #7 $169.30   13.369%   $191.9337   $191.93   $191.95   $191.90  
  7 purchase totals = $944.36       $1,044.3447   $1,044.34   $1,044.35   $1,044.30