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 $91.86   5.715%   $97.1098   $97.11   $97.10   $97.10  
  Purchase #2 $170.78   3.513%   $176.7795   $176.78   $176.80   $176.80  
  Purchase #3 $235.83   4.462%   $246.3527   $246.35   $246.35   $246.40  
  Purchase #4 $184.83   3.127%   $190.6096   $190.61   $190.60   $190.60  
  Purchase #5 $99.49   7.570%   $107.0214   $107.02   $107.00   $107.00  
  Purchase #6 $137.78   13.150%   $155.8981   $155.90   $155.90   $155.90  
  Purchase #7 $76.73   9.271%   $83.8436   $83.84   $83.85   $83.80  
  7 purchase totals = $997.30       $1,057.6147   $1,057.61   $1,057.60   $1,057.60