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 $181.95   7.592%   $195.7636   $195.76   $195.75   $195.80  
  Purchase #2 $15.27   8.872%   $16.6248   $16.62   $16.60   $16.60  
  Purchase #3 $8.28   7.519%   $8.9026   $8.90   $8.90   $8.90  
  Purchase #4 $221.42   6.351%   $235.4824   $235.48   $235.50   $235.50  
  Purchase #5 $169.99   6.770%   $181.4983   $181.50   $181.50   $181.50  
  Purchase #6 $233.52   6.533%   $248.7759   $248.78   $248.80   $248.80  
  Purchase #7 $105.74   11.636%   $118.0439   $118.04   $118.05   $118.00  
  7 purchase totals = $936.17       $1,005.0915   $1,005.08   $1,005.10   $1,005.10