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 $189.34   4.734%   $198.3034   $198.30   $198.30   $198.30  
  Purchase #2 $88.39   4.425%   $92.3013   $92.30   $92.30   $92.30  
  Purchase #3 $32.41   10.439%   $35.7933   $35.79   $35.80   $35.80  
  Purchase #4 $106.72   13.833%   $121.4826   $121.48   $121.50   $121.50  
  Purchase #5 $175.72   12.169%   $197.1034   $197.10   $197.10   $197.10  
  Purchase #6 $235.44   5.722%   $248.9119   $248.91   $248.90   $248.90  
  Purchase #7 $216.28   4.327%   $225.6384   $225.64   $225.65   $225.60  
  7 purchase totals = $1,044.30       $1,119.5343   $1,119.52   $1,119.55   $1,119.50