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 $148.93   13.503%   $169.04   $169.04   $169.05   $169.00  
  Purchase #2 $56.25   12.666%   $63.3746   $63.37   $63.35   $63.40  
  Purchase #3 $188.67   13.433%   $214.014   $214.01   $214.00   $214.00  
  Purchase #4 $111.69   11.116%   $124.1055   $124.11   $124.10   $124.10  
  Purchase #5 $77.59   11.682%   $86.6541   $86.65   $86.65   $86.70  
  Purchase #6 $25.66   5.519%   $27.0762   $27.08   $27.10   $27.10  
  Purchase #7 $155.50   11.706%   $173.7028   $173.70   $173.70   $173.70  
  7 purchase totals = $764.29       $857.9672   $857.96   $857.95   $858.00