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 $246.52   11.836%   $275.6981   $275.70   $275.70   $275.70  
  Purchase #2 $52.84   3.558%   $54.72   $54.72   $54.70   $54.70  
  Purchase #3 $39.35   11.203%   $43.7584   $43.76   $43.75   $43.80  
  Purchase #4 $165.49   7.865%   $178.5058   $178.51   $178.50   $178.50  
  Purchase #5 $49.72   12.854%   $56.111   $56.11   $56.10   $56.10  
  Purchase #6 $84.25   4.143%   $87.7405   $87.74   $87.75   $87.70  
  Purchase #7 $36.58   7.722%   $39.4047   $39.40   $39.40   $39.40  
  7 purchase totals = $674.75       $735.9385   $735.94   $735.90   $735.90