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 $67.61   5.364%   $71.2366   $71.24   $71.25   $71.20  
  Purchase #2 $77.97   9.810%   $85.6189   $85.62   $85.60   $85.60  
  Purchase #3 $167.42   7.548%   $180.0569   $180.06   $180.05   $180.10  
  Purchase #4 $155.62   7.296%   $166.974   $166.97   $166.95   $167.00  
  Purchase #5 $87.92   11.867%   $98.3535   $98.35   $98.35   $98.40  
  Purchase #6 $173.75   13.265%   $196.7979   $196.80   $196.80   $196.80  
  Purchase #7 $16.86   9.590%   $18.4769   $18.48   $18.50   $18.50  
  7 purchase totals = $747.15       $817.5147   $817.52   $817.50   $817.60