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 $148.71   5.783%   $157.3099   $157.31   $157.30   $157.30  
  Purchase #2 $113.58   5.671%   $120.0211   $120.02   $120.00   $120.00  
  Purchase #3 $56.72   11.135%   $63.0358   $63.04   $63.05   $63.00  
  Purchase #4 $15.73   6.456%   $16.7455   $16.75   $16.75   $16.70  
  Purchase #5 $239.54   5.607%   $252.971   $252.97   $252.95   $253.00  
  Purchase #6 $201.32   5.409%   $212.2094   $212.21   $212.20   $212.20  
  Purchase #7 $56.89   11.244%   $63.2867   $63.29   $63.30   $63.30  
  7 purchase totals = $832.49       $885.5794   $885.59   $885.55   $885.50