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 $67.47   11.166%   $75.0037   $75.00   $75.00   $75.00  
  Purchase #2 $234.68   8.223%   $253.9777   $253.98   $254.00   $254.00  
  Purchase #3 $161.95   8.728%   $176.085   $176.09   $176.10   $176.10  
  Purchase #4 $209.45   9.289%   $228.9058   $228.91   $228.90   $228.90  
  Purchase #5 $63.55   3.446%   $65.7399   $65.74   $65.75   $65.70  
  Purchase #6 $49.91   7.505%   $53.6557   $53.66   $53.65   $53.70  
  Purchase #7 $202.29   10.377%   $223.2816   $223.28   $223.30   $223.30  
  7 purchase totals = $989.30       $1,076.6494   $1,076.66   $1,076.70   $1,076.70