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 $198.52   13.853%   $226.021   $226.02   $226.00   $226.00  
  Purchase #2 $90.92   7.873%   $98.0781   $98.08   $98.10   $98.10  
  Purchase #3 $193.70   3.400%   $200.2858   $200.29   $200.30   $200.30  
  Purchase #4 $39.36   12.721%   $44.367   $44.37   $44.35   $44.40  
  Purchase #5 $20.94   8.782%   $22.779   $22.78   $22.80   $22.80  
  Purchase #6 $245.44   3.505%   $254.0427   $254.04   $254.05   $254.00  
  Purchase #7 $163.70   8.554%   $177.7029   $177.70   $177.70   $177.70  
  7 purchase totals = $952.58       $1,023.2765   $1,023.28   $1,023.30   $1,023.30