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 $24.98   6.252%   $26.5417   $26.54   $26.55   $26.50  
  Purchase #2 $237.56   8.107%   $256.819   $256.82   $256.80   $256.80  
  Purchase #3 $37.66   3.765%   $39.0779   $39.08   $39.10   $39.10  
  Purchase #4 $158.30   5.862%   $167.5795   $167.58   $167.60   $167.60  
  Purchase #5 $207.27   11.794%   $231.7154   $231.72   $231.70   $231.70  
  Purchase #6 $229.70   8.722%   $249.7344   $249.73   $249.75   $249.70  
  Purchase #7 $200.58   9.573%   $219.7815   $219.78   $219.80   $219.80  
  7 purchase totals = $1,096.05       $1,191.2494   $1,191.25   $1,191.30   $1,191.20