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 $183.84   11.560%   $205.0919   $205.09   $205.10   $205.10  
  Purchase #2 $43.26   3.441%   $44.7486   $44.75   $44.75   $44.70  
  Purchase #3 $99.26   4.833%   $104.0572   $104.06   $104.05   $104.10  
  Purchase #4 $202.65   11.456%   $225.8656   $225.87   $225.85   $225.90  
  Purchase #5 $30.89   6.513%   $32.9019   $32.90   $32.90   $32.90  
  Purchase #6 $193.87   6.222%   $205.9326   $205.93   $205.95   $205.90  
  Purchase #7 $241.51   11.362%   $268.9504   $268.95   $268.95   $269.00  
  7 purchase totals = $995.28       $1,087.5482   $1,087.55   $1,087.55   $1,087.60