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 $83.64   5.824%   $88.5112   $88.51   $88.50   $88.50  
  Purchase #2 $217.87   5.836%   $230.5849   $230.58   $230.60   $230.60  
  Purchase #3 $101.93   9.147%   $111.2535   $111.25   $111.25   $111.30  
  Purchase #4 $165.33   11.281%   $183.9809   $183.98   $184.00   $184.00  
  Purchase #5 $247.80   4.799%   $259.6919   $259.69   $259.70   $259.70  
  Purchase #6 $147.47   3.125%   $152.0784   $152.08   $152.10   $152.10  
  Purchase #7 $11.64   5.126%   $12.2367   $12.24   $12.25   $12.20  
  7 purchase totals = $975.68       $1,038.3375   $1,038.33   $1,038.40   $1,038.40