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 $176.69   13.764%   $201.0096   $201.01   $201.00   $201.00  
  Purchase #2 $31.48   5.826%   $33.314   $33.31   $33.30   $33.30  
  Purchase #3 $231.83   3.811%   $240.665   $240.67   $240.65   $240.70  
  Purchase #4 $230.80   6.787%   $246.4644   $246.46   $246.45   $246.50  
  Purchase #5 $89.48   13.247%   $101.3334   $101.33   $101.35   $101.30  
  Purchase #6 $75.46   10.747%   $83.5697   $83.57   $83.55   $83.60  
  Purchase #7 $249.62   13.204%   $282.5798   $282.58   $282.60   $282.60  
  7 purchase totals = $1,085.36       $1,188.9359   $1,188.93   $1,188.90   $1,189.00