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 $118.65   13.651%   $134.8469   $134.85   $134.85   $134.80  
  Purchase #2 $61.77   8.755%   $67.178   $67.18   $67.20   $67.20  
  Purchase #3 $60.25   12.171%   $67.583   $67.58   $67.60   $67.60  
  Purchase #4 $66.51   5.220%   $69.9818   $69.98   $70.00   $70.00  
  Purchase #5 $208.70   3.755%   $216.5367   $216.54   $216.55   $216.50  
  Purchase #6 $62.87   3.415%   $65.017   $65.02   $65.00   $65.00  
  Purchase #7 $27.37   6.123%   $29.0459   $29.05   $29.05   $29.00  
  7 purchase totals = $606.12       $650.1893   $650.20   $650.25   $650.10