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 $86.63   11.162%   $96.2996   $96.30   $96.30   $96.30  
  Purchase #2 $144.35   10.499%   $159.5053   $159.51   $159.50   $159.50  
  Purchase #3 $115.52   4.185%   $120.3545   $120.35   $120.35   $120.40  
  Purchase #4 $193.50   9.558%   $211.9947   $211.99   $212.00   $212.00  
  Purchase #5 $152.63   12.662%   $171.956   $171.96   $171.95   $172.00  
  Purchase #6 $14.83   8.186%   $16.044   $16.04   $16.05   $16.00  
  Purchase #7 $183.44   9.182%   $200.2835   $200.28   $200.30   $200.30  
  7 purchase totals = $890.90       $976.4376   $976.43   $976.45   $976.50