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 $229.82   10.511%   $253.9764   $253.98   $254.00   $254.00  
  Purchase #2 $99.78   7.490%   $107.2535   $107.25   $107.25   $107.30  
  Purchase #3 $126.44   7.145%   $135.4741   $135.47   $135.45   $135.50  
  Purchase #4 $196.97   3.482%   $203.8285   $203.83   $203.85   $203.80  
  Purchase #5 $106.93   10.721%   $118.394   $118.39   $118.40   $118.40  
  Purchase #6 $24.43   13.339%   $27.6887   $27.69   $27.70   $27.70  
  Purchase #7 $202.90   11.152%   $225.5274   $225.53   $225.55   $225.50  
  7 purchase totals = $987.27       $1,072.1426   $1,072.14   $1,072.20   $1,072.20