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 $118.46   13.460%   $134.4047   $134.40   $134.40   $134.40  
  Purchase #2 $122.50   12.395%   $137.6839   $137.68   $137.70   $137.70  
  Purchase #3 $173.35   7.839%   $186.9389   $186.94   $186.95   $186.90  
  Purchase #4 $87.69   10.602%   $96.9869   $96.99   $97.00   $97.00  
  Purchase #5 $182.82   11.281%   $203.4439   $203.44   $203.45   $203.40  
  Purchase #6 $68.59   8.790%   $74.6191   $74.62   $74.60   $74.60  
  Purchase #7 $216.31   7.523%   $232.583   $232.58   $232.60   $232.60  
  7 purchase totals = $969.72       $1,066.6604   $1,066.65   $1,066.70   $1,066.60