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 $79.79   6.842%   $85.2492   $85.25   $85.25   $85.20  
  Purchase #2 $63.25   3.128%   $65.2285   $65.23   $65.25   $65.20  
  Purchase #3 $60.78   10.167%   $66.9595   $66.96   $66.95   $67.00  
  Purchase #4 $25.71   10.305%   $28.3594   $28.36   $28.35   $28.40  
  Purchase #5 $80.97   10.563%   $89.5229   $89.52   $89.50   $89.50  
  Purchase #6 $195.65   3.142%   $201.7973   $201.80   $201.80   $201.80  
  Purchase #7 $26.91   12.360%   $30.2361   $30.24   $30.25   $30.20  
  7 purchase totals = $533.06       $567.3529   $567.36   $567.35   $567.30