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 $245.36   11.326%   $273.1495   $273.15   $273.15   $273.10  
  Purchase #2 $232.26   9.575%   $254.4989   $254.50   $254.50   $254.50  
  Purchase #3 $33.44   6.596%   $35.6457   $35.65   $35.65   $35.60  
  Purchase #4 $11.28   12.305%   $12.668   $12.67   $12.65   $12.70  
  Purchase #5 $149.51   7.358%   $160.5109   $160.51   $160.50   $160.50  
  Purchase #6 $56.35   5.257%   $59.3123   $59.31   $59.30   $59.30  
  Purchase #7 $235.78   11.678%   $263.3144   $263.31   $263.30   $263.30  
  7 purchase totals = $963.98       $1,059.0997   $1,059.10   $1,059.05   $1,059.00