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 $9.59   4.868%   $10.0568   $10.06   $10.05   $10.10  
  Purchase #2 $131.28   6.369%   $139.6412   $139.64   $139.65   $139.60  
  Purchase #3 $221.76   7.589%   $238.5894   $238.59   $238.60   $238.60  
  Purchase #4 $12.40   13.763%   $14.1066   $14.11   $14.10   $14.10  
  Purchase #5 $149.51   11.278%   $166.3717   $166.37   $166.35   $166.40  
  Purchase #6 $206.26   6.557%   $219.7845   $219.78   $219.80   $219.80  
  Purchase #7 $122.86   7.595%   $132.1912   $132.19   $132.20   $132.20  
  7 purchase totals = $853.66       $920.7414   $920.74   $920.75   $920.80