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 $229.93   7.433%   $247.0207   $247.02   $247.00   $247.00  
  Purchase #2 $116.83   11.447%   $130.2035   $130.20   $130.20   $130.20  
  Purchase #3 $55.65   4.130%   $57.9483   $57.95   $57.95   $57.90  
  Purchase #4 $43.79   7.413%   $47.0362   $47.04   $47.05   $47.00  
  Purchase #5 $132.34   12.219%   $148.5106   $148.51   $148.50   $148.50  
  Purchase #6 $223.91   11.144%   $248.8625   $248.86   $248.85   $248.90  
  Purchase #7 $165.86   7.216%   $177.8285   $177.83   $177.85   $177.80  
  7 purchase totals = $968.31       $1,057.4103   $1,057.41   $1,057.40   $1,057.30