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 $7.78   3.822%   $8.0774   $8.08   $8.10   $8.10  
  Purchase #2 $161.70   12.697%   $182.231   $182.23   $182.25   $182.20  
  Purchase #3 $247.99   6.282%   $263.5687   $263.57   $263.55   $263.60  
  Purchase #4 $43.56   11.525%   $48.5803   $48.58   $48.60   $48.60  
  Purchase #5 $147.40   9.608%   $161.5622   $161.56   $161.55   $161.60  
  Purchase #6 $119.79   8.300%   $129.7326   $129.73   $129.75   $129.70  
  Purchase #7 $120.36   13.119%   $136.15   $136.15   $136.15   $136.20  
  7 purchase totals = $848.58       $929.9022   $929.90   $929.95   $930.00