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 $48.43   9.368%   $52.9669   $52.97   $52.95   $53.00  
  Purchase #2 $96.68   12.195%   $108.4701   $108.47   $108.45   $108.50  
  Purchase #3 $233.92   13.621%   $265.7822   $265.78   $265.80   $265.80  
  Purchase #4 $156.80   4.722%   $164.2041   $164.20   $164.20   $164.20  
  Purchase #5 $213.59   11.276%   $237.6744   $237.67   $237.65   $237.70  
  Purchase #6 $135.49   4.432%   $141.4949   $141.49   $141.50   $141.50  
  Purchase #7 $65.90   10.382%   $72.7417   $72.74   $72.75   $72.70  
  7 purchase totals = $950.81       $1,043.3343   $1,043.32   $1,043.30   $1,043.40