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 $232.28   8.586%   $252.2236   $252.22   $252.20   $252.20  
  Purchase #2 $142.58   13.377%   $161.6529   $161.65   $161.65   $161.70  
  Purchase #3 $185.57   11.505%   $206.9198   $206.92   $206.90   $206.90  
  Purchase #4 $105.58   10.171%   $116.3185   $116.32   $116.30   $116.30  
  Purchase #5 $70.52   3.765%   $73.1751   $73.18   $73.20   $73.20  
  Purchase #6 $81.60   7.614%   $87.813   $87.81   $87.80   $87.80  
  Purchase #7 $96.55   9.837%   $106.0476   $106.05   $106.05   $106.00  
  7 purchase totals = $914.68       $1,004.1505   $1,004.15   $1,004.10   $1,004.10