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 $53.94   11.290%   $60.0298   $60.03   $60.05   $60.00  
  Purchase #2 $231.74   9.162%   $252.972   $252.97   $252.95   $253.00  
  Purchase #3 $207.33   11.288%   $230.7334   $230.73   $230.75   $230.70  
  Purchase #4 $123.89   4.751%   $129.776   $129.78   $129.80   $129.80  
  Purchase #5 $151.36   9.154%   $165.2155   $165.22   $165.20   $165.20  
  Purchase #6 $118.88   3.844%   $123.4497   $123.45   $123.45   $123.40  
  Purchase #7 $5.97   12.603%   $6.7224   $6.72   $6.70   $6.70  
  7 purchase totals = $893.11       $968.8988   $968.90   $968.90   $968.80