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 $201.55   11.271%   $224.2667   $224.27   $224.25   $224.30  
  Purchase #2 $189.94   9.691%   $208.3471   $208.35   $208.35   $208.30  
  Purchase #3 $32.84   3.300%   $33.9237   $33.92   $33.90   $33.90  
  Purchase #4 $183.98   10.150%   $202.654   $202.65   $202.65   $202.70  
  Purchase #5 $5.32   11.839%   $5.9498   $5.95   $5.95   $5.90  
  Purchase #6 $189.59   11.245%   $210.9094   $210.91   $210.90   $210.90  
  Purchase #7 $54.52   11.329%   $60.6966   $60.70   $60.70   $60.70  
  7 purchase totals = $857.74       $946.7473   $946.75   $946.70   $946.70