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 $53.29   13.817%   $60.6531   $60.65   $60.65   $60.70  
  Purchase #2 $243.35   12.266%   $273.1993   $273.20   $273.20   $273.20  
  Purchase #3 $30.39   12.869%   $34.3009   $34.30   $34.30   $34.30  
  Purchase #4 $228.54   10.713%   $253.0235   $253.02   $253.00   $253.00  
  Purchase #5 $191.97   6.777%   $204.9798   $204.98   $205.00   $205.00  
  Purchase #6 $122.99   9.552%   $134.738   $134.74   $134.75   $134.70  
  Purchase #7 $247.79   11.255%   $275.6788   $275.68   $275.70   $275.70  
  7 purchase totals = $1,118.32       $1,236.5734   $1,236.57   $1,236.60   $1,236.60