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 $236.50   11.737%   $264.258   $264.26   $264.25   $264.30  
  Purchase #2 $117.67   3.557%   $121.8555   $121.86   $121.85   $121.90  
  Purchase #3 $218.84   6.410%   $232.8676   $232.87   $232.85   $232.90  
  Purchase #4 $46.88   12.131%   $52.567   $52.57   $52.55   $52.60  
  Purchase #5 $113.25   4.372%   $118.2013   $118.20   $118.20   $118.20  
  Purchase #6 $165.39   13.654%   $187.9724   $187.97   $187.95   $188.00  
  Purchase #7 $194.44   12.454%   $218.6556   $218.66   $218.65   $218.70  
  7 purchase totals = $1,092.97       $1,196.3774   $1,196.39   $1,196.30   $1,196.60