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 $156.73   11.389%   $174.58   $174.58   $174.60   $174.60  
  Purchase #2 $196.90   11.718%   $219.9727   $219.97   $219.95   $220.00  
  Purchase #3 $83.32   11.585%   $92.9726   $92.97   $92.95   $93.00  
  Purchase #4 $92.91   9.847%   $102.0588   $102.06   $102.05   $102.10  
  Purchase #5 $132.73   13.860%   $151.1264   $151.13   $151.15   $151.10  
  Purchase #6 $105.32   9.155%   $114.962   $114.96   $114.95   $115.00  
  Purchase #7 $156.51   9.146%   $170.8244   $170.82   $170.80   $170.80  
  7 purchase totals = $924.42       $1,026.4969   $1,026.49   $1,026.45   $1,026.60