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 $61.29   3.693%   $63.5534   $63.55   $63.55   $63.60  
  Purchase #2 $106.90   3.415%   $110.5506   $110.55   $110.55   $110.60  
  Purchase #3 $83.79   11.576%   $93.4895   $93.49   $93.50   $93.50  
  Purchase #4 $67.25   9.204%   $73.4397   $73.44   $73.45   $73.40  
  Purchase #5 $211.36   6.718%   $225.5592   $225.56   $225.55   $225.60  
  Purchase #6 $161.68   4.321%   $168.6662   $168.67   $168.65   $168.70  
  Purchase #7 $211.62   6.864%   $226.1456   $226.15   $226.15   $226.10  
  7 purchase totals = $903.89       $961.4042   $961.41   $961.40   $961.50