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 $24.44   11.829%   $27.331   $27.33   $27.35   $27.30  
  Purchase #2 $194.98   9.840%   $214.166   $214.17   $214.15   $214.20  
  Purchase #3 $149.37   13.234%   $169.1376   $169.14   $169.15   $169.10  
  Purchase #4 $75.50   5.719%   $79.8178   $79.82   $79.80   $79.80  
  Purchase #5 $208.64   6.848%   $222.9277   $222.93   $222.95   $222.90  
  Purchase #6 $48.81   10.461%   $53.916   $53.92   $53.90   $53.90  
  Purchase #7 $243.57   6.141%   $258.5276   $258.53   $258.55   $258.50  
  7 purchase totals = $945.31       $1,025.8237   $1,025.84   $1,025.85   $1,025.70