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 $229.32   13.661%   $260.6474   $260.65   $260.65   $260.60  
  Purchase #2 $74.68   4.259%   $77.8606   $77.86   $77.85   $77.90  
  Purchase #3 $60.52   13.494%   $68.6866   $68.69   $68.70   $68.70  
  Purchase #4 $121.65   3.736%   $126.1948   $126.19   $126.20   $126.20  
  Purchase #5 $172.66   4.468%   $180.3744   $180.37   $180.35   $180.40  
  Purchase #6 $120.40   12.771%   $135.7763   $135.78   $135.80   $135.80  
  Purchase #7 $164.81   7.430%   $177.0554   $177.06   $177.05   $177.10  
  7 purchase totals = $944.04       $1,026.5955   $1,026.60   $1,026.60   $1,026.70