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 $169.83   10.558%   $187.7607   $187.76   $187.75   $187.80  
  Purchase #2 $68.64   12.592%   $77.2831   $77.28   $77.30   $77.30  
  Purchase #3 $237.79   8.145%   $257.158   $257.16   $257.15   $257.20  
  Purchase #4 $11.75   10.730%   $13.0108   $13.01   $13.00   $13.00  
  Purchase #5 $147.94   11.851%   $165.4724   $165.47   $165.45   $165.50  
  Purchase #6 $219.30   5.155%   $230.6049   $230.60   $230.60   $230.60  
  Purchase #7 $97.36   7.783%   $104.9375   $104.94   $104.95   $104.90  
  7 purchase totals = $952.61       $1,036.2274   $1,036.22   $1,036.20   $1,036.30