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 $218.82   11.463%   $243.9033   $243.90   $243.90   $243.90  
  Purchase #2 $170.94   13.447%   $193.9263   $193.93   $193.95   $193.90  
  Purchase #3 $241.44   9.553%   $264.5048   $264.50   $264.50   $264.50  
  Purchase #4 $161.82   4.744%   $169.4967   $169.50   $169.50   $169.50  
  Purchase #5 $191.51   10.603%   $211.8158   $211.82   $211.80   $211.80  
  Purchase #6 $56.67   10.296%   $62.5047   $62.50   $62.50   $62.50  
  Purchase #7 $144.85   10.702%   $160.3518   $160.35   $160.35   $160.40  
  7 purchase totals = $1,186.05       $1,306.5034   $1,306.50   $1,306.50   $1,306.50