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 $58.83   11.346%   $65.5049   $65.50   $65.50   $65.50  
  Purchase #2 $216.29   7.231%   $231.9299   $231.93   $231.95   $231.90  
  Purchase #3 $147.86   12.746%   $166.7062   $166.71   $166.70   $166.70  
  Purchase #4 $232.34   8.496%   $252.0796   $252.08   $252.10   $252.10  
  Purchase #5 $193.91   11.837%   $216.8631   $216.86   $216.85   $216.90  
  Purchase #6 $124.89   4.402%   $130.3877   $130.39   $130.40   $130.40  
  Purchase #7 $19.34   8.270%   $20.9394   $20.94   $20.95   $20.90  
  7 purchase totals = $993.46       $1,084.4108   $1,084.41   $1,084.45   $1,084.40