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 $92.69   9.587%   $101.5762   $101.58   $101.60   $101.60  
  Purchase #2 $177.67   7.817%   $191.5585   $191.56   $191.55   $191.60  
  Purchase #3 $185.74   11.317%   $206.7602   $206.76   $206.75   $206.80  
  Purchase #4 $120.83   11.244%   $134.4161   $134.42   $134.40   $134.40  
  Purchase #5 $22.55   10.599%   $24.9401   $24.94   $24.95   $24.90  
  Purchase #6 $43.83   6.645%   $46.7425   $46.74   $46.75   $46.70  
  Purchase #7 $219.96   10.178%   $242.3475   $242.35   $242.35   $242.30  
  7 purchase totals = $863.27       $948.3411   $948.35   $948.35   $948.30