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 $157.75   8.841%   $171.6967   $171.70   $171.70   $171.70  
  Purchase #2 $151.53   9.188%   $165.4526   $165.45   $165.45   $165.50  
  Purchase #3 $24.59   8.633%   $26.7129   $26.71   $26.70   $26.70  
  Purchase #4 $244.97   9.321%   $267.8037   $267.80   $267.80   $267.80  
  Purchase #5 $169.70   6.121%   $180.0873   $180.09   $180.10   $180.10  
  Purchase #6 $11.96   4.769%   $12.5304   $12.53   $12.55   $12.50  
  Purchase #7 $97.70   4.772%   $102.3622   $102.36   $102.35   $102.40  
  7 purchase totals = $858.20       $926.6458   $926.64   $926.65   $926.70