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 $91.74   10.668%   $101.5268   $101.53   $101.55   $101.50  
  Purchase #2 $88.66   6.832%   $94.7173   $94.72   $94.70   $94.70  
  Purchase #3 $117.47   9.184%   $128.2584   $128.26   $128.25   $128.30  
  Purchase #4 $190.93   6.461%   $203.266   $203.27   $203.25   $203.30  
  Purchase #5 $166.65   6.207%   $176.994   $176.99   $177.00   $177.00  
  Purchase #6 $228.47   11.256%   $254.1866   $254.19   $254.20   $254.20  
  Purchase #7 $249.45   9.179%   $272.347   $272.35   $272.35   $272.30  
  7 purchase totals = $1,133.37       $1,231.2961   $1,231.31   $1,231.30   $1,231.30