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 $190.68   11.436%   $212.4862   $212.49   $212.50   $212.50  
  Purchase #2 $239.90   10.834%   $265.8908   $265.89   $265.90   $265.90  
  Purchase #3 $59.88   7.758%   $64.5255   $64.53   $64.55   $64.50  
  Purchase #4 $218.37   7.837%   $235.4837   $235.48   $235.50   $235.50  
  Purchase #5 $74.42   6.685%   $79.395   $79.40   $79.40   $79.40  
  Purchase #6 $56.71   5.671%   $59.926   $59.93   $59.95   $59.90  
  Purchase #7 $158.79   11.694%   $177.3589   $177.36   $177.35   $177.40  
  7 purchase totals = $998.75       $1,095.0661   $1,095.08   $1,095.15   $1,095.10