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 $54.85   12.207%   $61.5455   $61.55   $61.55   $61.50  
  Purchase #2 $243.58   3.713%   $252.6241   $252.62   $252.60   $252.60  
  Purchase #3 $229.54   11.808%   $256.6441   $256.64   $256.65   $256.60  
  Purchase #4 $212.99   11.580%   $237.6542   $237.65   $237.65   $237.70  
  Purchase #5 $76.74   12.843%   $86.5957   $86.60   $86.60   $86.60  
  Purchase #6 $121.51   3.321%   $125.5453   $125.55   $125.55   $125.50  
  Purchase #7 $65.52   12.848%   $73.938   $73.94   $73.95   $73.90  
  7 purchase totals = $1,004.73       $1,094.5469   $1,094.55   $1,094.55   $1,094.40