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 $215.78   7.598%   $232.175   $232.18   $232.20   $232.20  
  Purchase #2 $56.95   6.729%   $60.7822   $60.78   $60.80   $60.80  
  Purchase #3 $218.62   10.352%   $241.2515   $241.25   $241.25   $241.30  
  Purchase #4 $144.50   13.759%   $164.3818   $164.38   $164.40   $164.40  
  Purchase #5 $129.28   12.273%   $145.1465   $145.15   $145.15   $145.10  
  Purchase #6 $151.35   7.854%   $163.237   $163.24   $163.25   $163.20  
  Purchase #7 $210.25   8.783%   $228.7163   $228.72   $228.70   $228.70  
  7 purchase totals = $1,126.73       $1,235.6903   $1,235.70   $1,235.75   $1,235.70