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 $64.73   5.861%   $68.5238   $68.52   $68.50   $68.50  
  Purchase #2 $216.58   9.818%   $237.8438   $237.84   $237.85   $237.80  
  Purchase #3 $114.28   7.802%   $123.1961   $123.20   $123.20   $123.20  
  Purchase #4 $105.46   7.476%   $113.3442   $113.34   $113.35   $113.30  
  Purchase #5 $75.40   12.738%   $85.0045   $85.00   $85.00   $85.00  
  Purchase #6 $213.88   12.790%   $241.2353   $241.24   $241.25   $241.20  
  Purchase #7 $157.42   5.431%   $165.9695   $165.97   $165.95   $166.00  
  7 purchase totals = $947.75       $1,035.1172   $1,035.11   $1,035.10   $1,035.00