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 $192.93   9.575%   $211.403   $211.40   $211.40   $211.40  
  Purchase #2 $60.27   7.301%   $64.6703   $64.67   $64.65   $64.70  
  Purchase #3 $244.66   3.541%   $253.3234   $253.32   $253.30   $253.30  
  Purchase #4 $154.68   4.744%   $162.018   $162.02   $162.00   $162.00  
  Purchase #5 $215.81   9.208%   $235.6818   $235.68   $235.70   $235.70  
  Purchase #6 $194.30   12.559%   $218.7021   $218.70   $218.70   $218.70  
  Purchase #7 $190.45   11.615%   $212.5708   $212.57   $212.55   $212.60  
  7 purchase totals = $1,253.10       $1,358.3694   $1,358.36   $1,358.30   $1,358.40