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 $235.57   12.496%   $265.0068   $265.01   $265.00   $265.00  
  Purchase #2 $10.81   3.322%   $11.1691   $11.17   $11.15   $11.20  
  Purchase #3 $213.89   4.813%   $224.1845   $224.18   $224.20   $224.20  
  Purchase #4 $211.58   3.569%   $219.1313   $219.13   $219.15   $219.10  
  Purchase #5 $39.78   4.458%   $41.5534   $41.55   $41.55   $41.60  
  Purchase #6 $194.83   12.150%   $218.5018   $218.50   $218.50   $218.50  
  Purchase #7 $42.29   10.648%   $46.793   $46.79   $46.80   $46.80  
  7 purchase totals = $948.75       $1,026.3399   $1,026.33   $1,026.35   $1,026.40