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 $218.57   9.133%   $238.532   $238.53   $238.55   $238.50  
  Purchase #2 $41.77   13.225%   $47.2941   $47.29   $47.30   $47.30  
  Purchase #3 $28.65   8.154%   $30.9861   $30.99   $31.00   $31.00  
  Purchase #4 $119.94   12.167%   $134.5331   $134.53   $134.55   $134.50  
  Purchase #5 $61.47   6.803%   $65.6518   $65.65   $65.65   $65.70  
  Purchase #6 $202.97   11.236%   $225.7757   $225.78   $225.80   $225.80  
  Purchase #7 $238.28   6.234%   $253.1344   $253.13   $253.15   $253.10  
  7 purchase totals = $911.65       $995.9072   $995.90   $996.00   $995.90