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 $181.99   11.657%   $203.2046   $203.20   $203.20   $203.20  
  Purchase #2 $102.82   11.354%   $114.4942   $114.49   $114.50   $114.50  
  Purchase #3 $31.50   9.529%   $34.5016   $34.50   $34.50   $34.50  
  Purchase #4 $30.93   10.658%   $34.2265   $34.23   $34.25   $34.20  
  Purchase #5 $118.55   9.255%   $129.5218   $129.52   $129.50   $129.50  
  Purchase #6 $189.61   9.594%   $207.8012   $207.80   $207.80   $207.80  
  Purchase #7 $238.71   5.469%   $251.765   $251.77   $251.75   $251.80  
  7 purchase totals = $894.11       $975.5149   $975.51   $975.50   $975.50