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 $57.61   13.599%   $65.4444   $65.44   $65.45   $65.40  
  Purchase #2 $242.43   8.761%   $263.6693   $263.67   $263.65   $263.70  
  Purchase #3 $29.45   8.430%   $31.9326   $31.93   $31.95   $31.90  
  Purchase #4 $226.38   11.344%   $252.0605   $252.06   $252.05   $252.10  
  Purchase #5 $158.41   12.160%   $177.6727   $177.67   $177.65   $177.70  
  Purchase #6 $45.52   5.369%   $47.964   $47.96   $47.95   $48.00  
  Purchase #7 $149.92   3.620%   $155.3471   $155.35   $155.35   $155.30  
  7 purchase totals = $909.72       $994.0906   $994.08   $994.05   $994.10