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 $191.60   4.662%   $200.5324   $200.53   $200.55   $200.50  
  Purchase #2 $24.47   10.379%   $27.0097   $27.01   $27.00   $27.00  
  Purchase #3 $116.28   9.291%   $127.0836   $127.08   $127.10   $127.10  
  Purchase #4 $211.54   3.669%   $219.3014   $219.30   $219.30   $219.30  
  Purchase #5 $142.65   8.610%   $154.9322   $154.93   $154.95   $154.90  
  Purchase #6 $43.39   6.608%   $46.2572   $46.26   $46.25   $46.30  
  Purchase #7 $211.36   3.840%   $219.4762   $219.48   $219.50   $219.50  
  7 purchase totals = $941.29       $994.5927   $994.59   $994.65   $994.60