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 $153.42   9.494%   $167.9857   $167.99   $168.00   $168.00  
  Purchase #2 $191.88   7.471%   $206.2154   $206.22   $206.20   $206.20  
  Purchase #3 $113.93   9.555%   $124.816   $124.82   $124.80   $124.80  
  Purchase #4 $128.93   3.533%   $133.4851   $133.49   $133.50   $133.50  
  Purchase #5 $79.27   9.533%   $86.8268   $86.83   $86.85   $86.80  
  Purchase #6 $189.37   9.651%   $207.6461   $207.65   $207.65   $207.60  
  Purchase #7 $103.31   3.788%   $107.2234   $107.22   $107.20   $107.20  
  7 purchase totals = $960.11       $1,034.1985   $1,034.22   $1,034.20   $1,034.10