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 $44.43   7.737%   $47.8675   $47.87   $47.85   $47.90  
  Purchase #2 $44.86   11.739%   $50.1261   $50.13   $50.15   $50.10  
  Purchase #3 $209.33   12.256%   $234.9855   $234.99   $235.00   $235.00  
  Purchase #4 $98.93   12.323%   $111.1211   $111.12   $111.10   $111.10  
  Purchase #5 $63.78   12.649%   $71.8475   $71.85   $71.85   $71.80  
  Purchase #6 $60.28   13.863%   $68.6366   $68.64   $68.65   $68.60  
  Purchase #7 $184.45   7.391%   $198.0827   $198.08   $198.10   $198.10  
  7 purchase totals = $706.06       $782.6670   $782.68   $782.70   $782.60