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 $188.39   6.865%   $201.323   $201.32   $201.30   $201.30  
  Purchase #2 $14.94   5.323%   $15.7353   $15.74   $15.75   $15.70  
  Purchase #3 $124.50   7.874%   $134.3031   $134.30   $134.30   $134.30  
  Purchase #4 $240.75   11.328%   $268.0222   $268.02   $268.00   $268.00  
  Purchase #5 $101.75   9.847%   $111.7693   $111.77   $111.75   $111.80  
  Purchase #6 $239.40   3.368%   $247.463   $247.46   $247.45   $247.50  
  Purchase #7 $65.36   10.341%   $72.1189   $72.12   $72.10   $72.10  
  7 purchase totals = $975.09       $1,050.7348   $1,050.73   $1,050.65   $1,050.70