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 $52.64   7.632%   $56.6575   $56.66   $56.65   $56.70  
  Purchase #2 $238.96   5.567%   $252.2629   $252.26   $252.25   $252.30  
  Purchase #3 $166.91   10.230%   $183.9849   $183.98   $184.00   $184.00  
  Purchase #4 $38.73   11.506%   $43.1863   $43.19   $43.20   $43.20  
  Purchase #5 $49.26   11.613%   $54.9806   $54.98   $55.00   $55.00  
  Purchase #6 $191.92   10.113%   $211.3289   $211.33   $211.35   $211.30  
  Purchase #7 $182.79   7.234%   $196.013   $196.01   $196.00   $196.00  
  7 purchase totals = $921.21       $998.4141   $998.41   $998.45   $998.50