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 $30.80   3.330%   $31.8256   $31.83   $31.85   $31.80  
  Purchase #2 $25.32   12.649%   $28.5227   $28.52   $28.50   $28.50  
  Purchase #3 $202.70   12.789%   $228.6233   $228.62   $228.60   $228.60  
  Purchase #4 $218.63   6.153%   $232.0823   $232.08   $232.10   $232.10  
  Purchase #5 $102.78   4.468%   $107.3722   $107.37   $107.35   $107.40  
  Purchase #6 $33.46   10.826%   $37.0824   $37.08   $37.10   $37.10  
  Purchase #7 $43.71   12.377%   $49.12   $49.12   $49.10   $49.10  
  7 purchase totals = $657.40       $714.6285   $714.62   $714.60   $714.60