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 $222.95   13.126%   $252.2144   $252.21   $252.20   $252.20  
  Purchase #2 $60.26   3.416%   $62.3185   $62.32   $62.30   $62.30  
  Purchase #3 $55.97   3.398%   $57.8719   $57.87   $57.85   $57.90  
  Purchase #4 $176.92   7.595%   $190.3571   $190.36   $190.35   $190.40  
  Purchase #5 $159.79   6.523%   $170.2131   $170.21   $170.20   $170.20  
  Purchase #6 $74.97   13.865%   $85.3646   $85.36   $85.35   $85.40  
  Purchase #7 $200.25   5.857%   $211.9786   $211.98   $212.00   $212.00  
  7 purchase totals = $951.11       $1,030.3182   $1,030.31   $1,030.25   $1,030.40