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 $59.69   8.217%   $64.5947   $64.59   $64.60   $64.60  
  Purchase #2 $19.45   6.170%   $20.6501   $20.65   $20.65   $20.70  
  Purchase #3 $178.54   7.366%   $191.6913   $191.69   $191.70   $191.70  
  Purchase #4 $154.68   8.648%   $168.0567   $168.06   $168.05   $168.10  
  Purchase #5 $198.52   13.200%   $224.7246   $224.72   $224.70   $224.70  
  Purchase #6 $114.62   7.293%   $122.9792   $122.98   $123.00   $123.00  
  Purchase #7 $150.84   6.625%   $160.8332   $160.83   $160.85   $160.80  
  7 purchase totals = $876.34       $953.5298   $953.52   $953.55   $953.60