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 $63.59   8.292%   $68.8629   $68.86   $68.85   $68.90  
  Purchase #2 $102.26   6.188%   $108.5878   $108.59   $108.60   $108.60  
  Purchase #3 $226.81   9.562%   $248.4976   $248.50   $248.50   $248.50  
  Purchase #4 $61.54   5.736%   $65.0699   $65.07   $65.05   $65.10  
  Purchase #5 $37.27   5.245%   $39.2248   $39.22   $39.20   $39.20  
  Purchase #6 $211.85   6.170%   $224.9211   $224.92   $224.90   $224.90  
  Purchase #7 $102.93   6.113%   $109.2221   $109.22   $109.20   $109.20  
  7 purchase totals = $806.25       $864.3862   $864.38   $864.30   $864.40