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 $246.36   5.282%   $259.3727   $259.37   $259.35   $259.40  
  Purchase #2 $128.31   11.331%   $142.8488   $142.85   $142.85   $142.80  
  Purchase #3 $8.41   13.850%   $9.5748   $9.57   $9.55   $9.60  
  Purchase #4 $190.54   13.180%   $215.6532   $215.65   $215.65   $215.70  
  Purchase #5 $96.91   3.453%   $100.2563   $100.26   $100.25   $100.30  
  Purchase #6 $155.97   8.462%   $169.1682   $169.17   $169.15   $169.20  
  Purchase #7 $199.52   8.380%   $216.2398   $216.24   $216.25   $216.20  
  7 purchase totals = $1,026.02       $1,113.1138   $1,113.11   $1,113.05   $1,113.20