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 $130.82   12.564%   $147.2562   $147.26   $147.25   $147.30  
  Purchase #2 $87.50   6.336%   $93.044   $93.04   $93.05   $93.00  
  Purchase #3 $164.66   6.830%   $175.9063   $175.91   $175.90   $175.90  
  Purchase #4 $31.48   12.136%   $35.3004   $35.30   $35.30   $35.30  
  Purchase #5 $182.75   4.814%   $191.5476   $191.55   $191.55   $191.50  
  Purchase #6 $221.34   3.751%   $229.6425   $229.64   $229.65   $229.60  
  Purchase #7 $148.79   11.278%   $165.5705   $165.57   $165.55   $165.60  
  7 purchase totals = $967.34       $1,038.2675   $1,038.27   $1,038.25   $1,038.20