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 $97.36   9.107%   $106.2266   $106.23   $106.25   $106.20  
  Purchase #2 $25.70   6.713%   $27.4252   $27.43   $27.45   $27.40  
  Purchase #3 $250.73   3.108%   $258.5227   $258.52   $258.50   $258.50  
  Purchase #4 $213.46   9.387%   $233.4975   $233.50   $233.50   $233.50  
  Purchase #5 $109.29   8.493%   $118.572   $118.57   $118.55   $118.60  
  Purchase #6 $172.52   9.585%   $189.056   $189.06   $189.05   $189.10  
  Purchase #7 $55.27   13.571%   $62.7707   $62.77   $62.75   $62.80  
  7 purchase totals = $924.33       $996.0707   $996.08   $996.05   $996.10