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 $134.96   13.846%   $153.6466   $153.65   $153.65   $153.60  
  Purchase #2 $184.76   9.224%   $201.8023   $201.80   $201.80   $201.80  
  Purchase #3 $46.44   4.819%   $48.6779   $48.68   $48.70   $48.70  
  Purchase #4 $173.34   4.551%   $181.2287   $181.23   $181.25   $181.20  
  Purchase #5 $177.34   11.772%   $198.2165   $198.22   $198.20   $198.20  
  Purchase #6 $45.37   12.119%   $50.8684   $50.87   $50.85   $50.90  
  Purchase #7 $233.32   4.114%   $242.9188   $242.92   $242.90   $242.90  
  7 purchase totals = $995.53       $1,077.3592   $1,077.37   $1,077.35   $1,077.30