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 $73.40   3.657%   $76.0842   $76.08   $76.10   $76.10  
  Purchase #2 $197.94   6.546%   $210.8972   $210.90   $210.90   $210.90  
  Purchase #3 $113.93   6.277%   $121.0814   $121.08   $121.10   $121.10  
  Purchase #4 $60.99   7.862%   $65.785   $65.79   $65.80   $65.80  
  Purchase #5 $239.73   13.106%   $271.149   $271.15   $271.15   $271.10  
  Purchase #6 $207.54   6.217%   $220.4428   $220.44   $220.45   $220.40  
  Purchase #7 $185.94   9.864%   $204.2811   $204.28   $204.30   $204.30  
  7 purchase totals = $1,079.47       $1,169.7207   $1,169.72   $1,169.80   $1,169.70