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 $247.61   8.386%   $268.3746   $268.37   $268.35   $268.40  
  Purchase #2 $137.40   4.415%   $143.4662   $143.47   $143.45   $143.50  
  Purchase #3 $181.86   8.148%   $196.678   $196.68   $196.70   $196.70  
  Purchase #4 $172.93   4.571%   $180.8346   $180.83   $180.85   $180.80  
  Purchase #5 $235.32   9.653%   $258.0354   $258.04   $258.05   $258.00  
  Purchase #6 $58.81   11.521%   $65.5855   $65.59   $65.60   $65.60  
  Purchase #7 $234.79   5.616%   $247.9758   $247.98   $248.00   $248.00  
  7 purchase totals = $1,268.72       $1,360.9501   $1,360.96   $1,361.00   $1,361.00