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 $37.81   9.520%   $41.4095   $41.41   $41.40   $41.40  
  Purchase #2 $96.99   7.159%   $103.9335   $103.93   $103.95   $103.90  
  Purchase #3 $59.58   7.386%   $63.9806   $63.98   $64.00   $64.00  
  Purchase #4 $224.61   12.460%   $252.5964   $252.60   $252.60   $252.60  
  Purchase #5 $250.56   10.774%   $277.5553   $277.56   $277.55   $277.60  
  Purchase #6 $240.65   6.136%   $255.4163   $255.42   $255.40   $255.40  
  Purchase #7 $201.40   9.335%   $220.2007   $220.20   $220.20   $220.20  
  7 purchase totals = $1,111.60       $1,215.0923   $1,215.10   $1,215.10   $1,215.10