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 $132.67   11.789%   $148.3105   $148.31   $148.30   $148.30  
  Purchase #2 $203.44   4.218%   $212.0211   $212.02   $212.00   $212.00  
  Purchase #3 $158.91   3.120%   $163.868   $163.87   $163.85   $163.90  
  Purchase #4 $165.59   9.442%   $181.225   $181.23   $181.25   $181.20  
  Purchase #5 $86.50   7.148%   $92.683   $92.68   $92.70   $92.70  
  Purchase #6 $248.61   11.645%   $277.5606   $277.56   $277.55   $277.60  
  Purchase #7 $227.44   9.304%   $248.601   $248.60   $248.60   $248.60  
  7 purchase totals = $1,223.16       $1,324.2692   $1,324.27   $1,324.25   $1,324.30