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 $53.67   5.521%   $56.6331   $56.63   $56.65   $56.60  
  Purchase #2 $95.95   6.136%   $101.8375   $101.84   $101.85   $101.80  
  Purchase #3 $172.76   13.435%   $195.9703   $195.97   $195.95   $196.00  
  Purchase #4 $116.40   12.751%   $131.2422   $131.24   $131.25   $131.20  
  Purchase #5 $63.79   3.706%   $66.1541   $66.15   $66.15   $66.20  
  Purchase #6 $101.52   4.739%   $106.331   $106.33   $106.35   $106.30  
  Purchase #7 $16.73   5.118%   $17.5862   $17.59   $17.60   $17.60  
  7 purchase totals = $620.82       $675.7544   $675.75   $675.80   $675.70