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 $152.30   11.587%   $169.947   $169.95   $169.95   $169.90  
  Purchase #2 $147.68   12.169%   $165.6512   $165.65   $165.65   $165.70  
  Purchase #3 $98.28   12.132%   $110.2033   $110.20   $110.20   $110.20  
  Purchase #4 $39.74   9.134%   $43.3699   $43.37   $43.35   $43.40  
  Purchase #5 $59.70   13.826%   $67.9541   $67.95   $67.95   $68.00  
  Purchase #6 $5.72   5.332%   $6.025   $6.03   $6.05   $6.00  
  Purchase #7 $216.80   3.794%   $225.0254   $225.03   $225.05   $225.00  
  7 purchase totals = $720.22       $788.1759   $788.18   $788.20   $788.20