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 $203.48   6.814%   $217.3451   $217.35   $217.35   $217.30  
  Purchase #2 $232.26   8.731%   $252.5386   $252.54   $252.55   $252.50  
  Purchase #3 $40.93   12.232%   $45.9366   $45.94   $45.95   $45.90  
  Purchase #4 $132.54   8.694%   $144.063   $144.06   $144.05   $144.10  
  Purchase #5 $157.50   11.527%   $175.655   $175.66   $175.65   $175.70  
  Purchase #6 $77.70   13.260%   $88.003   $88.00   $88.00   $88.00  
  Purchase #7 $88.62   6.186%   $94.102   $94.10   $94.10   $94.10  
  7 purchase totals = $933.03       $1,017.6433   $1,017.65   $1,017.65   $1,017.60