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 $144.45   12.629%   $162.6926   $162.69   $162.70   $162.70  
  Purchase #2 $213.44   7.131%   $228.6604   $228.66   $228.65   $228.70  
  Purchase #3 $82.29   6.502%   $87.6405   $87.64   $87.65   $87.60  
  Purchase #4 $224.97   13.125%   $254.4973   $254.50   $254.50   $254.50  
  Purchase #5 $209.30   12.333%   $235.113   $235.11   $235.10   $235.10  
  Purchase #6 $181.76   12.227%   $203.9838   $203.98   $204.00   $204.00  
  Purchase #7 $144.30   13.438%   $163.691   $163.69   $163.70   $163.70  
  7 purchase totals = $1,200.51       $1,336.2786   $1,336.27   $1,336.30   $1,336.30