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 $45.99   5.790%   $48.6528   $48.65   $48.65   $48.70  
  Purchase #2 $197.94   11.418%   $220.5408   $220.54   $220.55   $220.50  
  Purchase #3 $20.50   5.845%   $21.6982   $21.70   $21.70   $21.70  
  Purchase #4 $88.95   8.571%   $96.5739   $96.57   $96.55   $96.60  
  Purchase #5 $171.55   12.328%   $192.6987   $192.70   $192.70   $192.70  
  Purchase #6 $206.94   4.556%   $216.3682   $216.37   $216.35   $216.40  
  Purchase #7 $232.45   6.200%   $246.8619   $246.86   $246.85   $246.90  
  7 purchase totals = $964.32       $1,043.3945   $1,043.39   $1,043.35   $1,043.50