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 $223.82   10.609%   $247.5651   $247.57   $247.55   $247.60  
  Purchase #2 $169.58   4.145%   $176.6091   $176.61   $176.60   $176.60  
  Purchase #3 $145.55   8.227%   $157.5244   $157.52   $157.50   $157.50  
  Purchase #4 $50.85   7.150%   $54.4858   $54.49   $54.50   $54.50  
  Purchase #5 $162.52   9.352%   $177.7189   $177.72   $177.70   $177.70  
  Purchase #6 $141.86   7.184%   $152.0512   $152.05   $152.05   $152.10  
  Purchase #7 $64.50   4.702%   $67.5328   $67.53   $67.55   $67.50  
  7 purchase totals = $958.68       $1,033.4873   $1,033.49   $1,033.45   $1,033.50