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 $56.35   13.556%   $63.9888   $63.99   $64.00   $64.00  
  Purchase #2 $187.80   7.273%   $201.4587   $201.46   $201.45   $201.50  
  Purchase #3 $146.35   4.848%   $153.445   $153.45   $153.45   $153.40  
  Purchase #4 $246.65   4.388%   $257.473   $257.47   $257.45   $257.50  
  Purchase #5 $75.85   13.575%   $86.1466   $86.15   $86.15   $86.10  
  Purchase #6 $149.94   5.194%   $157.7279   $157.73   $157.75   $157.70  
  Purchase #7 $185.48   10.309%   $204.6011   $204.60   $204.60   $204.60  
  7 purchase totals = $1,048.42       $1,124.8411   $1,124.85   $1,124.85   $1,124.80