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 $158.93   6.334%   $168.9966   $169.00   $169.00   $169.00  
  Purchase #2 $179.81   11.598%   $200.6644   $200.66   $200.65   $200.70  
  Purchase #3 $92.26   5.741%   $97.5566   $97.56   $97.55   $97.60  
  Purchase #4 $49.76   12.139%   $55.8004   $55.80   $55.80   $55.80  
  Purchase #5 $73.50   11.210%   $81.7394   $81.74   $81.75   $81.70  
  Purchase #6 $53.52   11.860%   $59.8675   $59.87   $59.85   $59.90  
  Purchase #7 $186.75   5.467%   $196.9596   $196.96   $196.95   $197.00  
  7 purchase totals = $794.53       $861.5845   $861.59   $861.55   $861.70