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 $190.55   4.263%   $198.6731   $198.67   $198.65   $198.70  
  Purchase #2 $129.95   13.595%   $147.6167   $147.62   $147.60   $147.60  
  Purchase #3 $201.48   8.589%   $218.7851   $218.79   $218.80   $218.80  
  Purchase #4 $91.30   5.400%   $96.2302   $96.23   $96.25   $96.20  
  Purchase #5 $99.58   5.137%   $104.6954   $104.70   $104.70   $104.70  
  Purchase #6 $246.84   8.703%   $268.3225   $268.32   $268.30   $268.30  
  Purchase #7 $116.96   9.227%   $127.7519   $127.75   $127.75   $127.80  
  7 purchase totals = $1,076.66       $1,162.0749   $1,162.08   $1,162.05   $1,162.10