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 $200.33   6.789%   $213.9304   $213.93   $213.95   $213.90  
  Purchase #2 $203.46   11.280%   $226.4103   $226.41   $226.40   $226.40  
  Purchase #3 $79.48   4.535%   $83.0844   $83.08   $83.10   $83.10  
  Purchase #4 $76.97   12.140%   $86.3142   $86.31   $86.30   $86.30  
  Purchase #5 $140.64   3.820%   $146.0124   $146.01   $146.00   $146.00  
  Purchase #6 $60.82   13.252%   $68.8799   $68.88   $68.90   $68.90  
  Purchase #7 $174.62   11.570%   $194.8235   $194.82   $194.80   $194.80  
  7 purchase totals = $936.32       $1,019.4551   $1,019.44   $1,019.45   $1,019.40