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 $107.98   10.781%   $119.6213   $119.62   $119.60   $119.60  
  Purchase #2 $24.70   9.825%   $27.1268   $27.13   $27.15   $27.10  
  Purchase #3 $55.60   10.416%   $61.3913   $61.39   $61.40   $61.40  
  Purchase #4 $195.43   11.865%   $218.6178   $218.62   $218.60   $218.60  
  Purchase #5 $169.45   13.625%   $192.5376   $192.54   $192.55   $192.50  
  Purchase #6 $181.69   3.198%   $187.5004   $187.50   $187.50   $187.50  
  Purchase #7 $196.41   10.124%   $216.2945   $216.29   $216.30   $216.30  
  7 purchase totals = $931.26       $1,023.0897   $1,023.09   $1,023.10   $1,023.00