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 $124.93   7.506%   $134.3072   $134.31   $134.30   $134.30  
  Purchase #2 $231.68   8.347%   $251.0183   $251.02   $251.00   $251.00  
  Purchase #3 $54.70   10.832%   $60.6251   $60.63   $60.65   $60.60  
  Purchase #4 $177.49   11.497%   $197.896   $197.90   $197.90   $197.90  
  Purchase #5 $90.94   9.716%   $99.7757   $99.78   $99.80   $99.80  
  Purchase #6 $135.94   3.532%   $140.7414   $140.74   $140.75   $140.70  
  Purchase #7 $69.58   9.707%   $76.3341   $76.33   $76.35   $76.30  
  7 purchase totals = $885.26       $960.6978   $960.71   $960.75   $960.60