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 $211.55   3.826%   $219.6439   $219.64   $219.65   $219.60  
  Purchase #2 $106.62   4.392%   $111.3028   $111.30   $111.30   $111.30  
  Purchase #3 $248.87   3.865%   $258.4888   $258.49   $258.50   $258.50  
  Purchase #4 $196.69   12.362%   $221.0048   $221.00   $221.00   $221.00  
  Purchase #5 $224.67   9.778%   $246.6382   $246.64   $246.65   $246.60  
  Purchase #6 $64.37   6.492%   $68.5489   $68.55   $68.55   $68.50  
  Purchase #7 $130.32   11.760%   $145.6456   $145.65   $145.65   $145.60  
  7 purchase totals = $1,183.09       $1,271.2730   $1,271.27   $1,271.30   $1,271.10