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 $58.84   9.360%   $64.3474   $64.35   $64.35   $64.30  
  Purchase #2 $169.77   8.866%   $184.8218   $184.82   $184.80   $184.80  
  Purchase #3 $184.85   8.813%   $201.1408   $201.14   $201.15   $201.10  
  Purchase #4 $52.68   13.461%   $59.7713   $59.77   $59.75   $59.80  
  Purchase #5 $77.83   13.616%   $88.4273   $88.43   $88.45   $88.40  
  Purchase #6 $96.47   8.840%   $104.9979   $105.00   $105.00   $105.00  
  Purchase #7 $201.73   12.250%   $226.4419   $226.44   $226.45   $226.40  
  7 purchase totals = $842.17       $929.9484   $929.95   $929.95   $929.80