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 $212.54   3.853%   $220.7292   $220.73   $220.75   $220.70  
  Purchase #2 $15.47   5.675%   $16.3479   $16.35   $16.35   $16.30  
  Purchase #3 $44.67   4.153%   $46.5251   $46.53   $46.55   $46.50  
  Purchase #4 $17.45   9.281%   $19.0695   $19.07   $19.05   $19.10  
  Purchase #5 $246.62   10.413%   $272.3005   $272.30   $272.30   $272.30  
  Purchase #6 $201.77   10.869%   $223.7004   $223.70   $223.70   $223.70  
  Purchase #7 $245.28   3.372%   $253.5508   $253.55   $253.55   $253.60  
  7 purchase totals = $983.80       $1,052.2234   $1,052.23   $1,052.25   $1,052.20