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 $23.75   5.276%   $25.0031   $25.00   $25.00   $25.00  
  Purchase #2 $134.30   3.662%   $139.2181   $139.22   $139.20   $139.20  
  Purchase #3 $240.33   7.632%   $258.672   $258.67   $258.65   $258.70  
  Purchase #4 $179.73   12.771%   $202.6833   $202.68   $202.70   $202.70  
  Purchase #5 $153.37   9.283%   $167.6073   $167.61   $167.60   $167.60  
  Purchase #6 $126.28   9.815%   $138.6744   $138.67   $138.65   $138.70  
  Purchase #7 $96.64   7.141%   $103.5411   $103.54   $103.55   $103.50  
  7 purchase totals = $954.40       $1,035.3993   $1,035.39   $1,035.35   $1,035.40