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 $59.34   13.687%   $67.4619   $67.46   $67.45   $67.50  
  Purchase #2 $203.78   12.699%   $229.658   $229.66   $229.65   $229.70  
  Purchase #3 $150.62   12.566%   $169.5469   $169.55   $169.55   $169.50  
  Purchase #4 $239.82   5.297%   $252.5233   $252.52   $252.50   $252.50  
  Purchase #5 $186.38   6.570%   $198.6252   $198.63   $198.65   $198.60  
  Purchase #6 $21.92   11.445%   $24.4287   $24.43   $24.45   $24.40  
  Purchase #7 $229.33   5.803%   $242.638   $242.64   $242.65   $242.60  
  7 purchase totals = $1,091.19       $1,184.8820   $1,184.89   $1,184.90   $1,184.80