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 $38.48   13.231%   $43.5713   $43.57   $43.55   $43.60  
  Purchase #2 $247.69   6.271%   $263.2226   $263.22   $263.20   $263.20  
  Purchase #3 $52.68   11.262%   $58.6128   $58.61   $58.60   $58.60  
  Purchase #4 $218.31   9.352%   $238.7264   $238.73   $238.75   $238.70  
  Purchase #5 $168.39   7.205%   $180.5225   $180.52   $180.50   $180.50  
  Purchase #6 $32.92   5.537%   $34.7428   $34.74   $34.75   $34.70  
  Purchase #7 $116.52   5.603%   $123.0486   $123.05   $123.05   $123.00  
  7 purchase totals = $874.99       $942.4470   $942.44   $942.40   $942.30