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 $183.42   6.842%   $195.9696   $195.97   $195.95   $196.00  
  Purchase #2 $58.41   13.587%   $66.3462   $66.35   $66.35   $66.30  
  Purchase #3 $94.74   12.495%   $106.5778   $106.58   $106.60   $106.60  
  Purchase #4 $19.39   5.615%   $20.4787   $20.48   $20.50   $20.50  
  Purchase #5 $248.93   10.257%   $274.4628   $274.46   $274.45   $274.50  
  Purchase #6 $77.66   10.121%   $85.52   $85.52   $85.50   $85.50  
  Purchase #7 $24.84   12.743%   $28.0054   $28.01   $28.00   $28.00  
  7 purchase totals = $707.39       $777.3605   $777.37   $777.35   $777.40