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 $245.74   3.433%   $254.1763   $254.18   $254.20   $254.20  
  Purchase #2 $61.53   12.397%   $69.1579   $69.16   $69.15   $69.20  
  Purchase #3 $149.45   4.594%   $156.3157   $156.32   $156.30   $156.30  
  Purchase #4 $133.95   13.576%   $152.1351   $152.14   $152.15   $152.10  
  Purchase #5 $224.67   3.648%   $232.866   $232.87   $232.85   $232.90  
  Purchase #6 $134.33   4.758%   $140.7214   $140.72   $140.70   $140.70  
  Purchase #7 $54.95   11.789%   $61.4281   $61.43   $61.45   $61.40  
  7 purchase totals = $1,004.62       $1,066.8005   $1,066.82   $1,066.80   $1,066.80