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 $88.71   4.842%   $93.0053   $93.01   $93.00   $93.00  
  Purchase #2 $207.72   13.791%   $236.3667   $236.37   $236.35   $236.40  
  Purchase #3 $154.87   8.104%   $167.4207   $167.42   $167.40   $167.40  
  Purchase #4 $177.61   5.186%   $186.8209   $186.82   $186.80   $186.80  
  Purchase #5 $23.35   12.295%   $26.2209   $26.22   $26.20   $26.20  
  Purchase #6 $133.56   3.308%   $137.9782   $137.98   $138.00   $138.00  
  Purchase #7 $250.93   7.280%   $269.1977   $269.20   $269.20   $269.20  
  7 purchase totals = $1,036.75       $1,117.0104   $1,117.02   $1,116.95   $1,117.00