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 $93.52   10.708%   $103.5341   $103.53   $103.55   $103.50  
  Purchase #2 $196.53   9.188%   $214.5872   $214.59   $214.60   $214.60  
  Purchase #3 $42.31   9.669%   $46.401   $46.40   $46.40   $46.40  
  Purchase #4 $225.91   9.454%   $247.2675   $247.27   $247.25   $247.30  
  Purchase #5 $226.66   9.472%   $248.1292   $248.13   $248.15   $248.10  
  Purchase #6 $219.73   12.304%   $246.7656   $246.77   $246.75   $246.80  
  Purchase #7 $145.94   3.520%   $151.0771   $151.08   $151.10   $151.10  
  7 purchase totals = $1,150.60       $1,257.7617   $1,257.77   $1,257.80   $1,257.80