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 $181.34   8.581%   $196.9008   $196.90   $196.90   $196.90  
  Purchase #2 $22.31   7.509%   $23.9853   $23.99   $24.00   $24.00  
  Purchase #3 $45.75   12.242%   $51.3507   $51.35   $51.35   $51.40  
  Purchase #4 $168.88   9.451%   $184.8408   $184.84   $184.85   $184.80  
  Purchase #5 $157.39   8.543%   $170.8358   $170.84   $170.85   $170.80  
  Purchase #6 $158.94   4.799%   $166.5675   $166.57   $166.55   $166.60  
  Purchase #7 $194.53   3.137%   $200.6324   $200.63   $200.65   $200.60  
  7 purchase totals = $929.14       $995.1133   $995.12   $995.15   $995.10