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 $41.95   8.327%   $45.4432   $45.44   $45.45   $45.40  
  Purchase #2 $132.39   11.742%   $147.9352   $147.94   $147.95   $147.90  
  Purchase #3 $152.92   4.264%   $159.4405   $159.44   $159.45   $159.40  
  Purchase #4 $239.56   12.670%   $269.9123   $269.91   $269.90   $269.90  
  Purchase #5 $48.45   8.461%   $52.5494   $52.55   $52.55   $52.50  
  Purchase #6 $160.34   12.151%   $179.8229   $179.82   $179.80   $179.80  
  Purchase #7 $12.99   10.365%   $14.3364   $14.34   $14.35   $14.30  
  7 purchase totals = $788.60       $869.4399   $869.44   $869.45   $869.20