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 $168.52   9.755%   $184.9591   $184.96   $184.95   $185.00  
  Purchase #2 $88.26   7.244%   $94.6536   $94.65   $94.65   $94.70  
  Purchase #3 $190.65   10.823%   $211.284   $211.28   $211.30   $211.30  
  Purchase #4 $47.88   8.638%   $52.0159   $52.02   $52.00   $52.00  
  Purchase #5 $125.66   13.292%   $142.3627   $142.36   $142.35   $142.40  
  Purchase #6 $64.88   5.790%   $68.6366   $68.64   $68.65   $68.60  
  Purchase #7 $86.97   11.251%   $96.755   $96.76   $96.75   $96.80  
  7 purchase totals = $772.82       $850.6669   $850.67   $850.65   $850.80