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 $30.39   6.367%   $32.3249   $32.32   $32.30   $32.30  
  Purchase #2 $250.48   13.697%   $284.7882   $284.79   $284.80   $284.80  
  Purchase #3 $64.36   10.451%   $71.0863   $71.09   $71.10   $71.10  
  Purchase #4 $204.60   3.257%   $211.2638   $211.26   $211.25   $211.30  
  Purchase #5 $60.31   8.842%   $65.6426   $65.64   $65.65   $65.60  
  Purchase #6 $160.92   7.407%   $172.8393   $172.84   $172.85   $172.80  
  Purchase #7 $228.73   3.504%   $236.7447   $236.74   $236.75   $236.70  
  7 purchase totals = $999.79       $1,074.6898   $1,074.68   $1,074.70   $1,074.60