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 $123.96   3.639%   $128.4709   $128.47   $128.45   $128.50  
  Purchase #2 $161.45   6.657%   $172.1977   $172.20   $172.20   $172.20  
  Purchase #3 $193.63   10.593%   $214.1412   $214.14   $214.15   $214.10  
  Purchase #4 $43.69   4.798%   $45.7862   $45.79   $45.80   $45.80  
  Purchase #5 $192.44   9.118%   $209.9867   $209.99   $210.00   $210.00  
  Purchase #6 $141.86   10.559%   $156.839   $156.84   $156.85   $156.80  
  Purchase #7 $148.55   4.753%   $155.6106   $155.61   $155.60   $155.60  
  7 purchase totals = $1,005.58       $1,083.0323   $1,083.04   $1,083.05   $1,083.00