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 $8.71   11.404%   $9.7033   $9.70   $9.70   $9.70  
  Purchase #2 $230.25   8.808%   $250.5304   $250.53   $250.55   $250.50  
  Purchase #3 $233.76   5.219%   $245.9599   $245.96   $245.95   $246.00  
  Purchase #4 $162.42   10.529%   $179.5212   $179.52   $179.50   $179.50  
  Purchase #5 $126.78   11.454%   $141.3014   $141.30   $141.30   $141.30  
  Purchase #6 $23.42   6.601%   $24.966   $24.97   $24.95   $25.00  
  Purchase #7 $195.41   3.534%   $202.3158   $202.32   $202.30   $202.30  
  7 purchase totals = $980.75       $1,054.2980   $1,054.30   $1,054.25   $1,054.30