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 $92.96   12.195%   $104.2965   $104.30   $104.30   $104.30  
  Purchase #2 $226.93   7.104%   $243.0511   $243.05   $243.05   $243.10  
  Purchase #3 $10.96   7.594%   $11.7923   $11.79   $11.80   $11.80  
  Purchase #4 $135.74   4.199%   $141.4397   $141.44   $141.45   $141.40  
  Purchase #5 $158.72   4.338%   $165.6053   $165.61   $165.60   $165.60  
  Purchase #6 $109.61   8.253%   $118.6561   $118.66   $118.65   $118.70  
  Purchase #7 $197.72   8.793%   $215.1055   $215.11   $215.10   $215.10  
  7 purchase totals = $932.64       $999.9465   $999.96   $999.95   $1,000.00