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 $58.29   13.186%   $65.9761   $65.98   $66.00   $66.00  
  Purchase #2 $115.96   8.624%   $125.9604   $125.96   $125.95   $126.00  
  Purchase #3 $121.25   13.513%   $137.6345   $137.63   $137.65   $137.60  
  Purchase #4 $57.90   10.496%   $63.9772   $63.98   $64.00   $64.00  
  Purchase #5 $237.58   7.123%   $254.5028   $254.50   $254.50   $254.50  
  Purchase #6 $167.90   5.693%   $177.4585   $177.46   $177.45   $177.50  
  Purchase #7 $193.31   9.272%   $211.2337   $211.23   $211.25   $211.20  
  7 purchase totals = $952.19       $1,036.7432   $1,036.74   $1,036.80   $1,036.80