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 $60.82   12.234%   $68.2607   $68.26   $68.25   $68.30  
  Purchase #2 $106.41   8.772%   $115.7443   $115.74   $115.75   $115.70  
  Purchase #3 $167.28   10.111%   $184.1937   $184.19   $184.20   $184.20  
  Purchase #4 $58.64   3.764%   $60.8472   $60.85   $60.85   $60.80  
  Purchase #5 $139.31   5.728%   $147.2897   $147.29   $147.30   $147.30  
  Purchase #6 $18.87   4.625%   $19.7427   $19.74   $19.75   $19.70  
  Purchase #7 $118.77   13.260%   $134.5189   $134.52   $134.50   $134.50  
  7 purchase totals = $670.10       $730.5972   $730.59   $730.60   $730.50