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 $25.27   4.869%   $26.5004   $26.50   $26.50   $26.50  
  Purchase #2 $218.76   12.236%   $245.5275   $245.53   $245.55   $245.50  
  Purchase #3 $95.69   13.231%   $108.3507   $108.35   $108.35   $108.40  
  Purchase #4 $202.64   8.259%   $219.376   $219.38   $219.40   $219.40  
  Purchase #5 $172.68   12.524%   $194.3064   $194.31   $194.30   $194.30  
  Purchase #6 $24.31   13.728%   $27.6473   $27.65   $27.65   $27.60  
  Purchase #7 $214.86   12.275%   $241.2341   $241.23   $241.25   $241.20  
  7 purchase totals = $954.21       $1,062.9424   $1,062.95   $1,063.00   $1,062.90