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 $201.38   10.412%   $222.3477   $222.35   $222.35   $222.30  
  Purchase #2 $221.47   11.394%   $246.7043   $246.70   $246.70   $246.70  
  Purchase #3 $113.29   13.283%   $128.3383   $128.34   $128.35   $128.30  
  Purchase #4 $232.46   11.528%   $259.258   $259.26   $259.25   $259.30  
  Purchase #5 $99.69   9.335%   $108.9961   $109.00   $109.00   $109.00  
  Purchase #6 $86.85   7.828%   $93.6486   $93.65   $93.65   $93.60  
  Purchase #7 $43.36   4.657%   $45.3793   $45.38   $45.40   $45.40  
  7 purchase totals = $998.50       $1,104.6723   $1,104.68   $1,104.70   $1,104.60