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 $151.87   12.132%   $170.2949   $170.29   $170.30   $170.30  
  Purchase #2 $46.97   7.711%   $50.5919   $50.59   $50.60   $50.60  
  Purchase #3 $181.31   11.206%   $201.6276   $201.63   $201.65   $201.60  
  Purchase #4 $73.49   5.135%   $77.2637   $77.26   $77.25   $77.30  
  Purchase #5 $191.65   12.467%   $215.543   $215.54   $215.55   $215.50  
  Purchase #6 $166.50   11.444%   $185.5543   $185.55   $185.55   $185.60  
  Purchase #7 $243.26   9.145%   $265.5061   $265.51   $265.50   $265.50  
  7 purchase totals = $1,055.05       $1,166.3815   $1,166.37   $1,166.40   $1,166.40