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 $232.31   10.674%   $257.1068   $257.11   $257.10   $257.10  
  Purchase #2 $164.97   8.169%   $178.4464   $178.45   $178.45   $178.40  
  Purchase #3 $50.95   9.200%   $55.6374   $55.64   $55.65   $55.60  
  Purchase #4 $145.92   7.173%   $156.3868   $156.39   $156.40   $156.40  
  Purchase #5 $248.65   4.640%   $260.1874   $260.19   $260.20   $260.20  
  Purchase #6 $34.35   5.432%   $36.2159   $36.22   $36.20   $36.20  
  Purchase #7 $90.80   9.397%   $99.3325   $99.33   $99.35   $99.30  
  7 purchase totals = $967.95       $1,043.3132   $1,043.33   $1,043.35   $1,043.20