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 $91.84   10.841%   $101.7964   $101.80   $101.80   $101.80  
  Purchase #2 $55.61   12.142%   $62.3622   $62.36   $62.35   $62.40  
  Purchase #3 $50.42   5.293%   $53.0887   $53.09   $53.10   $53.10  
  Purchase #4 $136.53   6.180%   $144.9676   $144.97   $144.95   $145.00  
  Purchase #5 $95.62   5.684%   $101.055   $101.06   $101.05   $101.10  
  Purchase #6 $70.81   4.516%   $74.0078   $74.01   $74.00   $74.00  
  Purchase #7 $203.61   12.123%   $228.2936   $228.29   $228.30   $228.30  
  7 purchase totals = $704.44       $765.5713   $765.58   $765.55   $765.70