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 $48.34   12.412%   $54.34   $54.34   $54.35   $54.30  
  Purchase #2 $137.34   11.250%   $152.7908   $152.79   $152.80   $152.80  
  Purchase #3 $203.70   7.504%   $218.9856   $218.99   $219.00   $219.00  
  Purchase #4 $175.79   7.819%   $189.535   $189.54   $189.55   $189.50  
  Purchase #5 $226.49   5.802%   $239.6309   $239.63   $239.65   $239.60  
  Purchase #6 $144.86   3.856%   $150.4458   $150.45   $150.45   $150.40  
  Purchase #7 $58.38   7.239%   $62.6061   $62.61   $62.60   $62.60  
  7 purchase totals = $994.90       $1,068.3342   $1,068.35   $1,068.40   $1,068.20