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 $169.48   9.796%   $186.0823   $186.08   $186.10   $186.10  
  Purchase #2 $63.91   5.671%   $67.5343   $67.53   $67.55   $67.50  
  Purchase #3 $120.66   11.590%   $134.6445   $134.64   $134.65   $134.60  
  Purchase #4 $147.77   12.623%   $166.423   $166.42   $166.40   $166.40  
  Purchase #5 $186.94   6.560%   $199.2033   $199.20   $199.20   $199.20  
  Purchase #6 $203.89   11.244%   $226.8154   $226.82   $226.80   $226.80  
  Purchase #7 $125.54   4.624%   $131.345   $131.35   $131.35   $131.30  
  7 purchase totals = $1,018.19       $1,112.0478   $1,112.04   $1,112.05   $1,111.90