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 $96.86   10.365%   $106.8995   $106.90   $106.90   $106.90  
  Purchase #2 $127.49   6.647%   $135.9643   $135.96   $135.95   $136.00  
  Purchase #3 $163.89   10.395%   $180.9264   $180.93   $180.95   $180.90  
  Purchase #4 $227.29   13.721%   $258.4765   $258.48   $258.50   $258.50  
  Purchase #5 $155.90   9.248%   $170.3176   $170.32   $170.30   $170.30  
  Purchase #6 $47.91   12.720%   $54.0042   $54.00   $54.00   $54.00  
  Purchase #7 $169.46   5.837%   $179.3514   $179.35   $179.35   $179.40  
  7 purchase totals = $988.80       $1,085.9399   $1,085.94   $1,085.95   $1,086.00