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 $64.77   5.580%   $68.3842   $68.38   $68.40   $68.40  
  Purchase #2 $74.65   9.813%   $81.9754   $81.98   $82.00   $82.00  
  Purchase #3 $155.93   12.728%   $175.7768   $175.78   $175.80   $175.80  
  Purchase #4 $138.28   13.435%   $156.8579   $156.86   $156.85   $156.90  
  Purchase #5 $52.88   11.556%   $58.9908   $58.99   $59.00   $59.00  
  Purchase #6 $212.79   13.861%   $242.2848   $242.28   $242.30   $242.30  
  Purchase #7 $116.88   6.345%   $124.296   $124.30   $124.30   $124.30  
  7 purchase totals = $816.18       $908.5659   $908.57   $908.65   $908.70