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 $179.44   5.122%   $188.6309   $188.63   $188.65   $188.60  
  Purchase #2 $163.52   5.782%   $172.9747   $172.97   $172.95   $173.00  
  Purchase #3 $80.81   8.426%   $87.6191   $87.62   $87.60   $87.60  
  Purchase #4 $37.39   4.608%   $39.1129   $39.11   $39.10   $39.10  
  Purchase #5 $150.42   12.581%   $169.3443   $169.34   $169.35   $169.30  
  Purchase #6 $19.55   4.108%   $20.3531   $20.35   $20.35   $20.40  
  Purchase #7 $191.93   9.867%   $210.8677   $210.87   $210.85   $210.90  
  7 purchase totals = $823.06       $888.9027   $888.89   $888.85   $888.90