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 $62.28   5.654%   $65.8013   $65.80   $65.80   $65.80  
  Purchase #2 $179.90   6.176%   $191.0106   $191.01   $191.00   $191.00  
  Purchase #3 $86.70   12.183%   $97.2627   $97.26   $97.25   $97.30  
  Purchase #4 $102.97   3.689%   $106.7686   $106.77   $106.75   $106.80  
  Purchase #5 $171.87   6.551%   $183.1292   $183.13   $183.15   $183.10  
  Purchase #6 $169.37   6.507%   $180.3909   $180.39   $180.40   $180.40  
  Purchase #7 $173.74   5.131%   $182.6546   $182.65   $182.65   $182.70  
  7 purchase totals = $946.83       $1,007.0179   $1,007.01   $1,007.00   $1,007.10