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 $233.28   13.459%   $264.6772   $264.68   $264.70   $264.70  
  Purchase #2 $206.80   9.269%   $225.9683   $225.97   $225.95   $226.00  
  Purchase #3 $167.29   12.622%   $188.4053   $188.41   $188.40   $188.40  
  Purchase #4 $90.33   9.770%   $99.1552   $99.16   $99.15   $99.20  
  Purchase #5 $179.77   6.348%   $191.1818   $191.18   $191.20   $191.20  
  Purchase #6 $92.95   3.265%   $95.9848   $95.98   $96.00   $96.00  
  Purchase #7 $24.46   8.239%   $26.4753   $26.48   $26.50   $26.50  
  7 purchase totals = $994.88       $1,091.8479   $1,091.86   $1,091.90   $1,092.00