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 $24.74   7.609%   $26.6225   $26.62   $26.60   $26.60  
  Purchase #2 $201.42   12.242%   $226.0778   $226.08   $226.10   $226.10  
  Purchase #3 $102.57   11.673%   $114.543   $114.54   $114.55   $114.50  
  Purchase #4 $183.79   4.304%   $191.7003   $191.70   $191.70   $191.70  
  Purchase #5 $129.92   13.231%   $147.1097   $147.11   $147.10   $147.10  
  Purchase #6 $223.93   9.262%   $244.6704   $244.67   $244.65   $244.70  
  Purchase #7 $227.83   6.763%   $243.2381   $243.24   $243.25   $243.20  
  7 purchase totals = $1,094.20       $1,193.9618   $1,193.96   $1,193.95   $1,193.90