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 $61.51   7.486%   $66.1146   $66.11   $66.10   $66.10  
  Purchase #2 $95.27   12.147%   $106.8424   $106.84   $106.85   $106.80  
  Purchase #3 $14.63   12.826%   $16.5064   $16.51   $16.50   $16.50  
  Purchase #4 $124.37   9.548%   $136.2448   $136.24   $136.25   $136.20  
  Purchase #5 $246.28   3.629%   $255.2175   $255.22   $255.20   $255.20  
  Purchase #6 $53.25   6.132%   $56.5153   $56.52   $56.50   $56.50  
  Purchase #7 $139.96   9.397%   $153.112   $153.11   $153.10   $153.10  
  7 purchase totals = $735.27       $790.5530   $790.55   $790.50   $790.40