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 $248.89   11.255%   $276.9026   $276.90   $276.90   $276.90  
  Purchase #2 $97.74   13.513%   $110.9476   $110.95   $110.95   $110.90  
  Purchase #3 $59.49   9.521%   $65.154   $65.15   $65.15   $65.20  
  Purchase #4 $136.31   4.652%   $142.6511   $142.65   $142.65   $142.70  
  Purchase #5 $192.95   8.681%   $209.7   $209.70   $209.70   $209.70  
  Purchase #6 $243.91   7.421%   $262.0106   $262.01   $262.00   $262.00  
  Purchase #7 $227.96   6.753%   $243.3541   $243.35   $243.35   $243.40  
  7 purchase totals = $1,207.25       $1,310.7200   $1,310.71   $1,310.70   $1,310.80