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 $51.82   12.422%   $58.2571   $58.26   $58.25   $58.30  
  Purchase #2 $136.62   7.833%   $147.3214   $147.32   $147.30   $147.30  
  Purchase #3 $68.85   11.835%   $76.9984   $77.00   $77.00   $77.00  
  Purchase #4 $102.33   12.715%   $115.3413   $115.34   $115.35   $115.30  
  Purchase #5 $187.34   5.790%   $198.187   $198.19   $198.20   $198.20  
  Purchase #6 $147.75   13.614%   $167.8647   $167.86   $167.85   $167.90  
  Purchase #7 $190.59   10.870%   $211.3071   $211.31   $211.30   $211.30  
  7 purchase totals = $885.30       $975.2770   $975.28   $975.25   $975.30