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 $65.39   10.179%   $72.046   $72.05   $72.05   $72.00  
  Purchase #2 $53.31   6.807%   $56.9388   $56.94   $56.95   $56.90  
  Purchase #3 $208.57   11.489%   $232.5326   $232.53   $232.55   $232.50  
  Purchase #4 $177.79   13.791%   $202.309   $202.31   $202.30   $202.30  
  Purchase #5 $195.90   7.186%   $209.9774   $209.98   $210.00   $210.00  
  Purchase #6 $103.30   13.774%   $117.5285   $117.53   $117.55   $117.50  
  Purchase #7 $50.61   12.661%   $57.0177   $57.02   $57.00   $57.00  
  7 purchase totals = $854.87       $948.3500   $948.36   $948.40   $948.20