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 $204.37   12.115%   $229.1294   $229.13   $229.15   $229.10  
  Purchase #2 $132.84   6.788%   $141.8572   $141.86   $141.85   $141.90  
  Purchase #3 $171.80   7.446%   $184.5922   $184.59   $184.60   $184.60  
  Purchase #4 $111.59   8.499%   $121.074   $121.07   $121.05   $121.10  
  Purchase #5 $195.58   10.113%   $215.359   $215.36   $215.35   $215.40  
  Purchase #6 $42.82   11.339%   $47.6754   $47.68   $47.70   $47.70  
  Purchase #7 $60.34   3.402%   $62.3928   $62.39   $62.40   $62.40  
  7 purchase totals = $919.34       $1,002.0800   $1,002.08   $1,002.10   $1,002.20