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 $234.52   12.118%   $262.9391   $262.94   $262.95   $262.90  
  Purchase #2 $39.55   9.765%   $43.4121   $43.41   $43.40   $43.40  
  Purchase #3 $211.38   9.608%   $231.6894   $231.69   $231.70   $231.70  
  Purchase #4 $114.49   12.769%   $129.1092   $129.11   $129.10   $129.10  
  Purchase #5 $187.44   8.721%   $203.7866   $203.79   $203.80   $203.80  
  Purchase #6 $58.99   4.257%   $61.5012   $61.50   $61.50   $61.50  
  Purchase #7 $152.25   8.251%   $164.8121   $164.81   $164.80   $164.80  
  7 purchase totals = $998.62       $1,097.2497   $1,097.25   $1,097.25   $1,097.20