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 $167.60   9.194%   $183.0091   $183.01   $183.00   $183.00  
  Purchase #2 $184.69   4.411%   $192.8367   $192.84   $192.85   $192.80  
  Purchase #3 $237.26   5.765%   $250.938   $250.94   $250.95   $250.90  
  Purchase #4 $64.97   11.582%   $72.4948   $72.49   $72.50   $72.50  
  Purchase #5 $169.48   7.702%   $182.5333   $182.53   $182.55   $182.50  
  Purchase #6 $212.44   3.248%   $219.3401   $219.34   $219.35   $219.30  
  Purchase #7 $79.42   5.427%   $83.7301   $83.73   $83.75   $83.70  
  7 purchase totals = $1,115.86       $1,184.8821   $1,184.88   $1,184.95   $1,184.70