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 $208.67   12.428%   $234.6035   $234.60   $234.60   $234.60  
  Purchase #2 $5.72   6.131%   $6.0707   $6.07   $6.05   $6.10  
  Purchase #3 $219.47   12.506%   $246.9169   $246.92   $246.90   $246.90  
  Purchase #4 $222.60   4.379%   $232.3477   $232.35   $232.35   $232.30  
  Purchase #5 $11.56   13.313%   $13.099   $13.10   $13.10   $13.10  
  Purchase #6 $172.74   12.108%   $193.6554   $193.66   $193.65   $193.70  
  Purchase #7 $82.25   6.172%   $87.3265   $87.33   $87.35   $87.30  
  7 purchase totals = $923.01       $1,014.0197   $1,014.03   $1,014.00   $1,014.00