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 $90.49   6.557%   $96.4234   $96.42   $96.40   $96.40  
  Purchase #2 $220.77   11.386%   $245.9069   $245.91   $245.90   $245.90  
  Purchase #3 $44.63   10.524%   $49.3269   $49.33   $49.35   $49.30  
  Purchase #4 $135.60   8.437%   $147.0406   $147.04   $147.05   $147.00  
  Purchase #5 $135.28   7.262%   $145.104   $145.10   $145.10   $145.10  
  Purchase #6 $216.81   13.498%   $246.075   $246.08   $246.10   $246.10  
  Purchase #7 $87.40   9.370%   $95.5894   $95.59   $95.60   $95.60  
  7 purchase totals = $930.98       $1,025.4662   $1,025.47   $1,025.50   $1,025.40