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 $167.95   6.693%   $179.1909   $179.19   $179.20   $179.20  
  Purchase #2 $217.95   13.186%   $246.6889   $246.69   $246.70   $246.70  
  Purchase #3 $225.75   5.469%   $238.0963   $238.10   $238.10   $238.10  
  Purchase #4 $216.59   13.271%   $245.3337   $245.33   $245.35   $245.30  
  Purchase #5 $58.28   9.422%   $63.7711   $63.77   $63.75   $63.80  
  Purchase #6 $74.53   12.179%   $83.607   $83.61   $83.60   $83.60  
  Purchase #7 $12.99   8.845%   $14.139   $14.14   $14.15   $14.10  
  7 purchase totals = $974.04       $1,070.8269   $1,070.83   $1,070.85   $1,070.80