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 $54.48   13.294%   $61.7226   $61.72   $61.70   $61.70  
  Purchase #2 $75.73   12.653%   $85.3121   $85.31   $85.30   $85.30  
  Purchase #3 $227.64   13.320%   $257.9616   $257.96   $257.95   $258.00  
  Purchase #4 $247.60   3.320%   $255.8203   $255.82   $255.80   $255.80  
  Purchase #5 $208.71   11.330%   $232.3568   $232.36   $232.35   $232.40  
  Purchase #6 $34.77   9.149%   $37.9511   $37.95   $37.95   $38.00  
  Purchase #7 $87.31   9.591%   $95.6839   $95.68   $95.70   $95.70  
  7 purchase totals = $936.24       $1,026.8084   $1,026.80   $1,026.75   $1,026.90