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 $49.71   12.692%   $56.0192   $56.02   $56.00   $56.00  
  Purchase #2 $91.31   13.298%   $103.4524   $103.45   $103.45   $103.50  
  Purchase #3 $67.26   11.484%   $74.9841   $74.98   $75.00   $75.00  
  Purchase #4 $210.45   5.763%   $222.5782   $222.58   $222.60   $222.60  
  Purchase #5 $200.54   5.729%   $212.0289   $212.03   $212.05   $212.00  
  Purchase #6 $154.70   7.502%   $166.3056   $166.31   $166.30   $166.30  
  Purchase #7 $171.49   3.493%   $177.4801   $177.48   $177.50   $177.50  
  7 purchase totals = $945.46       $1,012.8485   $1,012.85   $1,012.90   $1,012.90