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 $6.84   4.819%   $7.1696   $7.17   $7.15   $7.20  
  Purchase #2 $168.58   3.613%   $174.6708   $174.67   $174.65   $174.70  
  Purchase #3 $136.51   12.445%   $153.4987   $153.50   $153.50   $153.50  
  Purchase #4 $240.25   5.327%   $253.0481   $253.05   $253.05   $253.00  
  Purchase #5 $83.42   13.860%   $94.982   $94.98   $95.00   $95.00  
  Purchase #6 $59.88   5.139%   $62.9572   $62.96   $62.95   $63.00  
  Purchase #7 $108.79   4.405%   $113.5822   $113.58   $113.60   $113.60  
  7 purchase totals = $804.27       $859.9086   $859.91   $859.90   $860.00