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 $206.29   9.548%   $225.9866   $225.99   $226.00   $226.00  
  Purchase #2 $212.38   12.849%   $239.6687   $239.67   $239.65   $239.70  
  Purchase #3 $52.73   11.860%   $58.9838   $58.98   $59.00   $59.00  
  Purchase #4 $235.36   3.122%   $242.7079   $242.71   $242.70   $242.70  
  Purchase #5 $39.56   11.778%   $44.2194   $44.22   $44.20   $44.20  
  Purchase #6 $193.40   9.676%   $212.1134   $212.11   $212.10   $212.10  
  Purchase #7 $169.25   4.866%   $177.4857   $177.49   $177.50   $177.50  
  7 purchase totals = $1,108.97       $1,201.1655   $1,201.17   $1,201.15   $1,201.20