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 $110.43   13.429%   $125.2596   $125.26   $125.25   $125.30  
  Purchase #2 $171.49   3.605%   $177.6722   $177.67   $177.65   $177.70  
  Purchase #3 $135.43   11.505%   $151.0112   $151.01   $151.00   $151.00  
  Purchase #4 $42.82   3.168%   $44.1765   $44.18   $44.20   $44.20  
  Purchase #5 $191.52   3.408%   $198.047   $198.05   $198.05   $198.00  
  Purchase #6 $127.42   6.418%   $135.5978   $135.60   $135.60   $135.60  
  Purchase #7 $152.77   10.123%   $168.2349   $168.23   $168.25   $168.20  
  7 purchase totals = $931.88       $999.9992   $1,000.00   $1,000.00   $1,000.00