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 $94.95   8.261%   $102.7938   $102.79   $102.80   $102.80  
  Purchase #2 $171.98   11.234%   $191.3002   $191.30   $191.30   $191.30  
  Purchase #3 $155.31   11.747%   $173.5543   $173.55   $173.55   $173.60  
  Purchase #4 $248.35   10.129%   $273.5054   $273.51   $273.50   $273.50  
  Purchase #5 $215.49   11.798%   $240.9135   $240.91   $240.90   $240.90  
  Purchase #6 $12.37   10.750%   $13.6998   $13.70   $13.70   $13.70  
  Purchase #7 $17.40   7.342%   $18.6775   $18.68   $18.70   $18.70  
  7 purchase totals = $915.85       $1,014.4445   $1,014.44   $1,014.45   $1,014.50