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 $63.79   5.718%   $67.4375   $67.44   $67.45   $67.40  
  Purchase #2 $225.90   9.661%   $247.7242   $247.72   $247.70   $247.70  
  Purchase #3 $15.48   7.187%   $16.5925   $16.59   $16.60   $16.60  
  Purchase #4 $126.96   12.360%   $142.6523   $142.65   $142.65   $142.70  
  Purchase #5 $172.52   11.606%   $192.5427   $192.54   $192.55   $192.50  
  Purchase #6 $69.37   7.655%   $74.6803   $74.68   $74.70   $74.70  
  Purchase #7 $227.36   10.217%   $250.5894   $250.59   $250.60   $250.60  
  7 purchase totals = $901.38       $992.2189   $992.21   $992.25   $992.20