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 $205.51   8.626%   $223.2373   $223.24   $223.25   $223.20  
  Purchase #2 $57.61   4.825%   $60.3897   $60.39   $60.40   $60.40  
  Purchase #3 $55.51   9.607%   $60.8428   $60.84   $60.85   $60.80  
  Purchase #4 $43.46   3.110%   $44.8116   $44.81   $44.80   $44.80  
  Purchase #5 $122.33   4.241%   $127.518   $127.52   $127.50   $127.50  
  Purchase #6 $126.49   7.364%   $135.8047   $135.80   $135.80   $135.80  
  Purchase #7 $116.25   4.186%   $121.1162   $121.12   $121.10   $121.10  
  7 purchase totals = $727.16       $773.7203   $773.72   $773.70   $773.60