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 $167.37   4.565%   $175.0104   $175.01   $175.00   $175.00  
  Purchase #2 $108.25   10.663%   $119.7927   $119.79   $119.80   $119.80  
  Purchase #3 $218.33   3.119%   $225.1397   $225.14   $225.15   $225.10  
  Purchase #4 $114.76   6.821%   $122.5878   $122.59   $122.60   $122.60  
  Purchase #5 $89.72   7.577%   $96.5181   $96.52   $96.50   $96.50  
  Purchase #6 $23.31   6.134%   $24.7398   $24.74   $24.75   $24.70  
  Purchase #7 $10.62   12.815%   $11.981   $11.98   $12.00   $12.00  
  7 purchase totals = $732.36       $775.7695   $775.77   $775.80   $775.70