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 $227.84   11.605%   $254.2808   $254.28   $254.30   $254.30  
  Purchase #2 $91.41   10.760%   $101.2457   $101.25   $101.25   $101.20  
  Purchase #3 $109.97   10.413%   $121.4212   $121.42   $121.40   $121.40  
  Purchase #4 $242.48   4.820%   $254.1675   $254.17   $254.15   $254.20  
  Purchase #5 $147.61   11.160%   $164.0833   $164.08   $164.10   $164.10  
  Purchase #6 $122.48   6.226%   $130.1056   $130.11   $130.10   $130.10  
  Purchase #7 $20.91   11.635%   $23.3429   $23.34   $23.35   $23.30  
  7 purchase totals = $962.70       $1,048.6470   $1,048.65   $1,048.65   $1,048.60