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 $237.51   6.778%   $253.6084   $253.61   $253.60   $253.60  
  Purchase #2 $48.95   11.679%   $54.6669   $54.67   $54.65   $54.70  
  Purchase #3 $112.75   13.102%   $127.5225   $127.52   $127.50   $127.50  
  Purchase #4 $90.65   4.570%   $94.7927   $94.79   $94.80   $94.80  
  Purchase #5 $147.85   6.564%   $157.5549   $157.55   $157.55   $157.60  
  Purchase #6 $193.51   4.444%   $202.1096   $202.11   $202.10   $202.10  
  Purchase #7 $117.50   5.734%   $124.2375   $124.24   $124.25   $124.20  
  7 purchase totals = $948.72       $1,014.4925   $1,014.49   $1,014.45   $1,014.50