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 $31.44   8.569%   $34.1341   $34.13   $34.15   $34.10  
  Purchase #2 $180.59   6.614%   $192.5342   $192.53   $192.55   $192.50  
  Purchase #3 $211.98   11.498%   $236.3535   $236.35   $236.35   $236.40  
  Purchase #4 $148.81   4.564%   $155.6017   $155.60   $155.60   $155.60  
  Purchase #5 $180.61   12.584%   $203.338   $203.34   $203.35   $203.30  
  Purchase #6 $177.58   3.331%   $183.4952   $183.50   $183.50   $183.50  
  Purchase #7 $63.78   13.602%   $72.4554   $72.46   $72.45   $72.50  
  7 purchase totals = $994.79       $1,077.9121   $1,077.91   $1,077.95   $1,077.90