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 $149.61   7.833%   $161.329   $161.33   $161.35   $161.30  
  Purchase #2 $155.28   4.789%   $162.7164   $162.72   $162.70   $162.70  
  Purchase #3 $145.64   3.345%   $150.5117   $150.51   $150.50   $150.50  
  Purchase #4 $245.93   9.711%   $269.8123   $269.81   $269.80   $269.80  
  Purchase #5 $20.80   12.179%   $23.3332   $23.33   $23.35   $23.30  
  Purchase #6 $107.37   12.242%   $120.5142   $120.51   $120.50   $120.50  
  Purchase #7 $61.29   5.559%   $64.6971   $64.70   $64.70   $64.70  
  7 purchase totals = $885.92       $952.9139   $952.91   $952.90   $952.80