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 $224.82   3.456%   $232.5898   $232.59   $232.60   $232.60  
  Purchase #2 $137.40   13.184%   $155.5148   $155.51   $155.50   $155.50  
  Purchase #3 $41.58   7.286%   $44.6095   $44.61   $44.60   $44.60  
  Purchase #4 $235.30   12.782%   $265.376   $265.38   $265.40   $265.40  
  Purchase #5 $82.72   3.694%   $85.7757   $85.78   $85.80   $85.80  
  Purchase #6 $161.96   3.257%   $167.235   $167.24   $167.25   $167.20  
  Purchase #7 $43.77   13.110%   $49.5082   $49.51   $49.50   $49.50  
  7 purchase totals = $927.55       $1,000.6090   $1,000.62   $1,000.65   $1,000.60