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 $145.65   5.839%   $154.1545   $154.15   $154.15   $154.20  
  Purchase #2 $51.98   5.447%   $54.8114   $54.81   $54.80   $54.80  
  Purchase #3 $101.35   5.466%   $106.8898   $106.89   $106.90   $106.90  
  Purchase #4 $89.73   7.681%   $96.6222   $96.62   $96.60   $96.60  
  Purchase #5 $200.26   3.147%   $206.5622   $206.56   $206.55   $206.60  
  Purchase #6 $202.98   9.336%   $221.9302   $221.93   $221.95   $221.90  
  Purchase #7 $48.97   11.268%   $54.4879   $54.49   $54.50   $54.50  
  7 purchase totals = $840.92       $895.4582   $895.45   $895.45   $895.50