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 $57.26   3.132%   $59.0534   $59.05   $59.05   $59.10  
  Purchase #2 $159.30   12.695%   $179.5231   $179.52   $179.50   $179.50  
  Purchase #3 $130.39   12.737%   $146.9978   $147.00   $147.00   $147.00  
  Purchase #4 $76.44   10.611%   $84.551   $84.55   $84.55   $84.60  
  Purchase #5 $248.40   11.556%   $277.1051   $277.11   $277.10   $277.10  
  Purchase #6 $74.50   7.695%   $80.2328   $80.23   $80.25   $80.20  
  Purchase #7 $110.74   7.384%   $118.917   $118.92   $118.90   $118.90  
  7 purchase totals = $857.03       $946.3802   $946.38   $946.35   $946.40