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 $68.81   6.274%   $73.1271   $73.13   $73.15   $73.10  
  Purchase #2 $211.78   6.801%   $226.1832   $226.18   $226.20   $226.20  
  Purchase #3 $150.68   6.466%   $160.423   $160.42   $160.40   $160.40  
  Purchase #4 $201.61   6.813%   $215.3457   $215.35   $215.35   $215.30  
  Purchase #5 $13.83   7.700%   $14.8949   $14.89   $14.90   $14.90  
  Purchase #6 $147.94   10.621%   $163.6527   $163.65   $163.65   $163.70  
  Purchase #7 $144.40   4.544%   $150.9615   $150.96   $150.95   $151.00  
  7 purchase totals = $939.05       $1,004.5881   $1,004.58   $1,004.60   $1,004.60