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 $184.33   13.485%   $209.1869   $209.19   $209.20   $209.20  
  Purchase #2 $108.64   8.293%   $117.6495   $117.65   $117.65   $117.60  
  Purchase #3 $72.39   11.348%   $80.6048   $80.60   $80.60   $80.60  
  Purchase #4 $113.94   7.776%   $122.8   $122.80   $122.80   $122.80  
  Purchase #5 $30.32   6.830%   $32.3909   $32.39   $32.40   $32.40  
  Purchase #6 $71.39   11.605%   $79.6748   $79.67   $79.65   $79.70  
  Purchase #7 $142.35   6.222%   $151.207   $151.21   $151.20   $151.20  
  7 purchase totals = $723.36       $793.5139   $793.51   $793.50   $793.50