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 $38.69   11.580%   $43.1703   $43.17   $43.15   $43.20  
  Purchase #2 $60.60   6.718%   $64.6711   $64.67   $64.65   $64.70  
  Purchase #3 $166.87   11.368%   $185.8398   $185.84   $185.85   $185.80  
  Purchase #4 $218.95   8.795%   $238.2067   $238.21   $238.20   $238.20  
  Purchase #5 $114.94   6.377%   $122.2697   $122.27   $122.25   $122.30  
  Purchase #6 $199.76   3.154%   $206.0604   $206.06   $206.05   $206.10  
  Purchase #7 $131.51   12.508%   $147.9593   $147.96   $147.95   $148.00  
  7 purchase totals = $931.32       $1,008.1773   $1,008.18   $1,008.10   $1,008.30