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 $167.28   8.731%   $181.8852   $181.89   $181.90   $181.90  
  Purchase #2 $178.99   3.143%   $184.6157   $184.62   $184.60   $184.60  
  Purchase #3 $203.91   9.234%   $222.739   $222.74   $222.75   $222.70  
  Purchase #4 $30.55   3.229%   $31.5365   $31.54   $31.55   $31.50  
  Purchase #5 $116.64   7.178%   $125.0124   $125.01   $125.00   $125.00  
  Purchase #6 $140.75   13.720%   $160.0609   $160.06   $160.05   $160.10  
  Purchase #7 $104.73   11.662%   $116.9436   $116.94   $116.95   $116.90  
  7 purchase totals = $942.85       $1,022.7933   $1,022.80   $1,022.80   $1,022.70