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 $224.73   13.354%   $254.7404   $254.74   $254.75   $254.70  
  Purchase #2 $23.65   3.253%   $24.4193   $24.42   $24.40   $24.40  
  Purchase #3 $124.91   9.392%   $136.6415   $136.64   $136.65   $136.60  
  Purchase #4 $216.94   12.416%   $243.8753   $243.88   $243.90   $243.90  
  Purchase #5 $209.58   6.780%   $223.7895   $223.79   $223.80   $223.80  
  Purchase #6 $175.32   11.660%   $195.7623   $195.76   $195.75   $195.80  
  Purchase #7 $13.98   3.694%   $14.4964   $14.50   $14.50   $14.50  
  7 purchase totals = $989.11       $1,093.7247   $1,093.73   $1,093.75   $1,093.70