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 $143.53   6.431%   $152.7604   $152.76   $152.75   $152.80  
  Purchase #2 $23.99   3.311%   $24.7843   $24.78   $24.80   $24.80  
  Purchase #3 $211.35   13.751%   $240.4127   $240.41   $240.40   $240.40  
  Purchase #4 $54.56   7.180%   $58.4774   $58.48   $58.50   $58.50  
  Purchase #5 $54.50   12.662%   $61.4008   $61.40   $61.40   $61.40  
  Purchase #6 $74.27   9.343%   $81.209   $81.21   $81.20   $81.20  
  Purchase #7 $236.86   6.644%   $252.597   $252.60   $252.60   $252.60  
  7 purchase totals = $799.06       $871.6416   $871.64   $871.65   $871.70