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 $250.26   5.752%   $264.655   $264.66   $264.65   $264.70  
  Purchase #2 $244.44   13.585%   $277.6472   $277.65   $277.65   $277.60  
  Purchase #3 $80.67   13.310%   $91.4072   $91.41   $91.40   $91.40  
  Purchase #4 $142.92   12.389%   $160.6264   $160.63   $160.65   $160.60  
  Purchase #5 $141.31   9.349%   $154.5211   $154.52   $154.50   $154.50  
  Purchase #6 $114.58   4.605%   $119.8564   $119.86   $119.85   $119.90  
  Purchase #7 $20.88   3.148%   $21.5373   $21.54   $21.55   $21.50  
  7 purchase totals = $995.06       $1,090.2506   $1,090.27   $1,090.25   $1,090.20