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 $54.48   8.279%   $58.9904   $58.99   $59.00   $59.00  
  Purchase #2 $228.37   10.640%   $252.6686   $252.67   $252.65   $252.70  
  Purchase #3 $91.50   6.566%   $97.5079   $97.51   $97.50   $97.50  
  Purchase #4 $35.43   8.302%   $38.3714   $38.37   $38.35   $38.40  
  Purchase #5 $174.81   6.605%   $186.3562   $186.36   $186.35   $186.40  
  Purchase #6 $160.82   10.757%   $178.1194   $178.12   $178.10   $178.10  
  Purchase #7 $62.39   4.310%   $65.079   $65.08   $65.10   $65.10  
  7 purchase totals = $807.80       $877.0929   $877.10   $877.05   $877.20