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 $80.47   5.873%   $85.196   $85.20   $85.20   $85.20  
  Purchase #2 $96.55   4.688%   $101.0763   $101.08   $101.10   $101.10  
  Purchase #3 $203.90   10.673%   $225.6622   $225.66   $225.65   $225.70  
  Purchase #4 $232.66   6.307%   $247.3339   $247.33   $247.35   $247.30  
  Purchase #5 $106.73   8.585%   $115.8928   $115.89   $115.90   $115.90  
  Purchase #6 $107.79   8.771%   $117.2443   $117.24   $117.25   $117.20  
  Purchase #7 $111.72   6.672%   $119.174   $119.17   $119.15   $119.20  
  7 purchase totals = $939.82       $1,011.5795   $1,011.57   $1,011.60   $1,011.60