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 $188.74   7.484%   $202.8653   $202.87   $202.85   $202.90  
  Purchase #2 $250.82   6.617%   $267.4168   $267.42   $267.40   $267.40  
  Purchase #3 $59.61   4.750%   $62.4415   $62.44   $62.45   $62.40  
  Purchase #4 $236.79   11.313%   $263.5781   $263.58   $263.60   $263.60  
  Purchase #5 $8.58   12.495%   $9.6521   $9.65   $9.65   $9.70  
  Purchase #6 $173.58   6.711%   $185.229   $185.23   $185.25   $185.20  
  Purchase #7 $48.30   7.656%   $51.9978   $52.00   $52.00   $52.00  
  7 purchase totals = $966.42       $1,043.1806   $1,043.19   $1,043.20   $1,043.20