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 $117.76   3.467%   $121.8427   $121.84   $121.85   $121.80  
  Purchase #2 $196.37   4.252%   $204.7197   $204.72   $204.70   $204.70  
  Purchase #3 $179.25   6.394%   $190.7112   $190.71   $190.70   $190.70  
  Purchase #4 $84.92   8.681%   $92.2919   $92.29   $92.30   $92.30  
  Purchase #5 $241.79   12.547%   $272.1274   $272.13   $272.15   $272.10  
  Purchase #6 $23.66   9.832%   $25.9863   $25.99   $26.00   $26.00  
  Purchase #7 $130.64   12.617%   $147.1228   $147.12   $147.10   $147.10  
  7 purchase totals = $974.39       $1,054.8020   $1,054.80   $1,054.80   $1,054.70