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 $62.85   4.277%   $65.5381   $65.54   $65.55   $65.50  
  Purchase #2 $203.88   12.531%   $229.4282   $229.43   $229.45   $229.40  
  Purchase #3 $28.40   4.694%   $29.7331   $29.73   $29.75   $29.70  
  Purchase #4 $162.77   10.637%   $180.0838   $180.08   $180.10   $180.10  
  Purchase #5 $188.79   13.430%   $214.1445   $214.14   $214.15   $214.10  
  Purchase #6 $190.97   3.533%   $197.717   $197.72   $197.70   $197.70  
  Purchase #7 $235.81   12.275%   $264.7557   $264.76   $264.75   $264.80  
  7 purchase totals = $1,073.47       $1,181.4004   $1,181.40   $1,181.45   $1,181.30