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 $49.65   5.639%   $52.4498   $52.45   $52.45   $52.40  
  Purchase #2 $198.43   6.258%   $210.8477   $210.85   $210.85   $210.80  
  Purchase #3 $103.28   8.226%   $111.7758   $111.78   $111.80   $111.80  
  Purchase #4 $146.37   13.464%   $166.0773   $166.08   $166.10   $166.10  
  Purchase #5 $59.91   11.442%   $66.7649   $66.76   $66.75   $66.80  
  Purchase #6 $152.75   9.722%   $167.6004   $167.60   $167.60   $167.60  
  Purchase #7 $69.35   5.621%   $73.2482   $73.25   $73.25   $73.20  
  7 purchase totals = $779.74       $848.7641   $848.77   $848.80   $848.70